Flexible tube for an endoscope

ABSTRACT

A flexible tube for an endoscope has an elongated tubular core body, and an outer cover which is provided over the core body. The outer cover is composed of an inner layer, an outer layer and at least one intermediate layer. In this flexible tube, any one of the layers is different from one of the other layers in its property. Further, at least one of the layers has a thickness-varying region where the thickness of the layer varies in its longitudinal direction. In addition, the inner layer of the outer cover has projections which are integrally formed on the inner layer so that the projections project into holes and/or the recesses formed on the core body. This structure makes it possible to produce a flexible tube for an endoscope that has high durability, high flexibility and high chemical resistance as well as excellent operationability.

This application is a divisional of U.S. patent application Ser. No.09/848,301, filed May 4, 2001 now U.S. Pat. No. 6,860,849, thedisclosure of which is expressly incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flexible tube for an endoscope.

2. Description of the Prior Art

Generally, a flexible tube for an endoscope has a structure whichincludes a tubular core obtained by covering the outer periphery of aspiral tube with a mesh tube and an outer cover formed of a syntheticresin or the like and provided over the outer periphery of the tubularcore.

In endoscopic examination, the flexible tube for an endoscope isinserted along the body cavity to a deep part such as the stomach,duodenum, small intestine, and large intestine. In order to perform theinserting operation easily and reliably, it is necessary for theflexible tube that a push-in force applied to the proximal end (sidecloser to the operator) of the flexible tube is fully transmitted to itsdistal end. However, if bucking occurs in the flexible tube, the push-inforce can not be fully transmitted to the distal end because the push-inforce is partially absorbed by the bent part where the buckling occurs.This means that such a flexible tube for an endoscope can not achievereliable inserting operation. In order to avoid the occurrence of suchbuckling, it is necessary for the flexible tube to have sufficientflexibility so that bending is hard to occur. Further, the outer covermust be firmly attached or bonded to the tubular core since buckling isliable to occur at areas where the outer cover is peeled off from thetubular core.

Furthermore, in order to perform the inserting operation reliably, it isalso necessary for the flexible tube that a rotational force (that is, atwist) applied to the proximal end thereof is fully transmitted to thedistal end thereof. In other word, a flexible tube for an endoscope isalso required to have satisfactory rotational followability.

Moreover, a flexible tube for an endoscope is also required to have arelatively high stiffness on the proximal end side (side closer to theoperator) and have a flexibility on the distal end side from theviewpoint of the operability and safety of insertion and reduction inthe burden on the patient.

Up to now, there are known several flexible tubes for an endoscope whichaim to improve the insertion operability in view of the problemsdescribed above. One of such flexible tubes is disclosed in JapaneseLaid-open Patent Applications No. Hei 5-50287, in which an outer coverof a flexible tube for an endoscope is constructed from a double layerstructure comprised of an outer layer made of a material having goodelasticity and an inner layer made of a material having good resiliency,thereby improving resiliency of the flexible tube as a whole. Otherexample of such flexible tube is disclosed in Japanese Patent No.2641789, in which a distal end side of the flexible tube is made of asoft elastomer and a proximal end side thereof is made of a hardelastomer so that the stiffness varies from the distal end side towardthe proximal end side.

However, in these prior arts described in the above, the bonding forcebetween the outer cover and the core has been left out of consideration,so that there is a case that the outer cover is peeled off from the coreafter repeated use, thus leading to the deterioration in flexibility andresistance to buckling of the flexible tube. In short, there is aproblem in the durability of the flexible tube for an endoscope.

Furthermore, although an endoscope must be cleaned and disinfected everytime when it is used, in the above prior arts no consideration is givento the chemical resistance of the outer covers. Consequently, in theseprior arts, deterioration proceeds during the repeated disinfections,which results in possibility of generation of fine cracks or the likeand peeling off of the outer cover from the core.

SUMMARY OF THE INVENTION

In view of the problems in the prior art described in the above, it isthe object of the present invention to provide a flexible tube for anendoscope that possesses various kinds of performances required for aflexible tube for an endoscope, in particular to provide a flexible tubefor an endoscope excellent in the operability of insertion, resistanceto chemicals and durability.

In order to achieve the above object, the present invention is directedto a flexible tube for an endoscope, comprising:

an elongated tubular core body; and

an outer cover which is provided over the core body, the outer coverhaving a portion which is formed into a laminate structure composed ofat least three layers.

In this invention, it is preferred that the layers of the laminatestructure include an inner layer, an outer layer and at least oneintermediate layer formed between the inner layer and the outer layer.

Further, in this invention, it is also preferred that the core body hasa plurality of holes and/or a plurality of recesses. In this case, it Ispreferred that the core body includes: a coil that is formed by windinga band-shaped material into a spiral form; and a reticular tube that isformed by weaving a plurality of fine wires together, the reticular tubebeing provided over the coil. Further, it is also preferred that theinner layer of the outer cover has projections which are integrallyformed on the inner layer so that the projections project into the holesand/or the recesses.

Furthermore, in this invention, it is also preferred that at least oneof the fine wires forming the reticular tube is coated with a syntheticresin so that a coating of the synthetic resin is provided on the finewire, in which at least a part of the coating is fused with and bondedto the inner layer of the outer cover.

Moreover, in this invention, it is also preferred that the inner layerof the outer cover contains a material having a compatibility with thesynthetic resin of the coating.

Further, in this invention, it is also preferred that the portion of thelaminate structure of the outer cover has a substantially uniformthickness over its entire region.

Furthermore, in this invention, it is also preferred that any one of theinner, outer and intermediate layers is different from one of the otherlayers in its physical property and/or chemical property.

Moreover, in this invention, it is also preferred that any one of theinner, outer and intermediate layers is different from one of the otherlayers in its hardness.

Moreover, in this invention, it is also preferred that the outer layerof the outer cover contains a material having resistance to chemical.

Moreover, in this invention, it is also preferred that the intermediatelayer of the outer cover is formed of a material having higherelasticity than that of the outer layer.

Moreover, in this invention, it is also preferred that the outer layerof the outer cover is formed of a material having higher hardness thanthat of any one of the inner and intermediate layers.

Moreover, in this invention, it is also preferred that at least a partof the outer layer of the outer cover has higher hardness than that ofany of the inner and intermediate layers.

Moreover, in this invention, it is also preferred that the intermediatelayer of the outer cover is formed so as to function as cushioning meansbetween the inner layer and the outer layer.

Moreover, in this invention, it is also preferred that at least one ofthe inner, outer and intermediate layers of the outer cover is formed ofa material that contains at least one selected from the group consistingof polyurethane-based elastomer, polyester-based elastomer,polyolefine-based elastomer, polystyrene-based elastomer,polyamide-based elastomer, fluorine-based elastomer, and fluororubber.

Moreover, in this invention, it is also preferred that each of theinner, outer and intermediate layers of the outer cover is formed of amaterial that contains at least one selected from the group consistingof polyurethane-based elastomer, polyester-based elastomer,polyolefine-based elastomer, polystyrene-based elastomer,polyamide-based elastomer, fluorine-based elastomer, and fluororubber.

Further, in this invention, it is also preferred that the outer cover isprovided over the core body through an extrusion molding process.

Furthermore, in this invention, it is also preferred that the flexibletube has tip and base ends, and flexibility of the flexible tubeincreases in a gradual or stepwise manner along the direction from thebase end toward the tip end.

Moreover, in this invention, it is also preferred that any one of thelayers constituting the portion of the laminate structure of the outercover is different from one of the other layers in its physical propertyand/or chemical property.

Moreover, in this invention, it is also preferred that any one of layersconstituting the laminate structure of the outer cover is different fromone of the other layers in hardness.

Moreover, in this invention, it is also preferred that at least one ofthe layers constituting the portion of the laminate structure has athickness-varying region where the thickness of the layer varies in itslongitudinal direction.

In this case, it is preferred that the thickness-varying region extendssubstantially over an entire region of the layer, and within thethickness-varying region the thickness of the layer varies in itslongitudinal direction in a gradual or stepwise manner.

Further, it is also preferred that the layer with the thickness-varyingregion has at least one uniform thickness region which is formed so asto adjoin the thickness-varying region.

Furthermore, it is also preferred that the layer having thethickness-varying region is formed of a material that is different frommaterials constituting the other layers in its hardness.

Moreover, it is also preferred that each of at least two of the layersconstituting the portion of the laminate structure has athickness-varying region where the thickness of the layer varies in itslongitudinal direction.

Moreover, it is also preferred that the outer cover is provided over thecore body through an extrusion molding process. In this case, it ispreferred that in the extrusion molding process a constituent materialfor each of the layers is fed at a predetermined feeding rate while thecore body is fed at a predetermined feeding speed, in which thethickness of the layer having the thickness-varying region is controlledby adjusting the feeding rate of the material for the layer during theextrusion molding process and/or adjusting the feeding speed of the corebody during the extrusion molding process.

Further, in this invention, it is preferred that at least one of thelayers constituting the portion of the laminate structure has at leasttwo regions and at least one boundary part along its longitudinaldirection, and one of the regions is contiguous to the other regionthrough the boundary part, in which one of the regions is different fromthe other regions adjacent thereto in its physical property and/orchemical property.

In this case, it is preferred that one of the regions is formed of amaterial which is different from that forming the other region adjacentthereto.

Further, it is also preferred that each of at least two of the layersconstituting the portion of the laminate structure has at least tworegions and at least one boundary part along its longitudinal direction,and one of the regions is contiguous to the other region through theboundary part, in which one of the regions is different from the otherregion adjacent thereto in its physical property and/or chemicalproperty. In this case, it is preferred that the outer cover is formedsuch that the boundary part of one layer is not located above or belowthe boundary part of the other layer in its thickness direction.

Furthermore, it is also preferred that the boundary part is formed as aproperty-varying part within which the physical property and/or thechemical property of the layer gradually vary in its longitudinaldirection. In this case, the boundary part is formed of a mixture of amaterial constituting one of the regions and a material constituting theother region.

Moreover, it is also preferred that the layer having the boundary partis formed such that the physical property and/or the chemical propertywithin the boundary part vary in its longitudinal direction in asubstantially stepwise manner.

Moreover, it is also preferred that in the layer having the at least tworegions, one of the regions is different from the other region adjacentthereto in its hardness.

Moreover, it is also preferred that the flexible tube has tip and baseends, and flexibility of the flexible tube increases in a gradual orstepwise manner along the direction from the base end to the tip end.

These and other objects, structures and advantages of the presentinvention will be apparent more clearly from the following descriptionof the invention based on the examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overall structure of an endoscope having a firstembodiment of a flexible tube according to the present invention;

FIG. 2 is a sectional view which shows a part of the flexible tube inFIG. 1;

FIG. 3 is a sectional view which shows a part of a second embodiment ofthe flexible tube according to the present invention;

FIG. 4 is a sectional view which shows a part of a third embodiment ofthe flexible tube according to the present invention;

FIG. 5 is a sectional view which shows a part of a fourth embodiment ofthe flexible tube according to the present invention;

FIG. 6 is a sectional view which shows a part of a fifth embodiment ofthe flexible tube according to the present invention;

FIG. 7 is a sectional view which shows a part of a sixth embodiment ofthe flexible tube according to the present invention;

FIG. 8 is a sectional view which shows a part of a seventh embodiment ofthe flexible tube according to the present invention;

FIG. 9 is a sectional view which shows a part of an eighth embodiment ofthe flexible tube according to the present invention;

FIG. 10 is a sectional view which shows a part of a ninth embodiment ofthe flexible tube according to the present invention;

FIG. 11 is a sectional view which shows a part of a tenth embodiment ofthe flexible tube according to the present invention;

FIG. 12 is a sectional view which shows a part of an eleventh embodimentof the flexible tube according to the present invention;

FIG. 13 is an illustration which shows a state where an flexible tube isdivided into eight sections;

FIG. 14 is an illustration which shows a state where an flexible tube isdivided into ninth sections; and

FIG. 15 is an illustration which shows a state where the bendingstiffness in one of the sections shown in FIG. 13 or 14 is measured.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, detailed description of the preferred embodiments of aflexible tube for an endoscope according to the present invention willbe given with reference to the appended drawings.

I. First Embodiment (Flexible Tube 1A)

(I-1) Overall-Structure of Electronic Endoscope

First, a first embodiment of the flexible tube for an endoscope will bedescribed-with reference to FIGS. 1 and 2. FIG. 1 shows an overallstructure of an electronic endoscope 10 (electronic scope) having aflexible tube 1A according to the present invention. FIG. 2 is asectional view which shows a part of the flexible tube 1A of theelectronic endoscope 10 in FIG. 1. In FIG. 2, the right-hand sidecorresponds to the base side (i.e., side closer to an operator), and theleft-hand side corresponds to the tip side of the electronic endoscope10.

In the following, the upper side and the lower side in FIG. 1 will bereferred to as “base” and “tip,” respectively. Further, the electronicendoscope will be referred to simply as an “endoscope.” Furthermore, theflexible tube for an endoscope will be referred to simply as a “flexibletube.”

As shown in FIG. 1, the endoscope 10 has an elongated flexible tube(insertion section) 1A designed to be inserted into a body cavity of aliving body; a bendable tube 5 provided on a tip end 12 of the flexibletube 1A; an operating section 6 provided on a base end 11 of theflexible tube 1A, which is gripped by an operator during an endoscopicexamination to manipulate the endoscope 10; a light guide flexible tube7 connected at one end thereof to the operating section 6; and a plug 8provided on the other end of the light guide flexible tube 7.

On the side faces of the operating section 6, there are providedoperating knobs 61 and 62. When changing the direction of the bendabletube 5 during the endoscopic examination, the operator turns each of theoperating knobs 61 and 62 to pull appropriately wires (not shown)arranged in the flexible tube 1A. In this way, the bendable tube 5 isbent to a desired direction.

The endoscope 10 has an imaging element (CCD) for taking an image of anobservation area, which is provided at the tip end of the bendable tube5. Further, the endoscope 10 has a connector 82 provided on one end ofthe plug 8. The connector 82 is connected to a light source device whichis connected to a monitor (not shown) via a cable.

In the endoscope 10, the reflected light (which forms an image of theobservation area) from the observation area is received by the imagingelement. Then, the imaging element outputs an image signal correspondingto the image formed on the imaging element by the reflected light. Theimage signal is transmitted to the plug 8 via an image signal cable (notshown in the drawing) which extends inside the bendable tube 5, theflexible tube 1A, the operating section 6 and the light guide flexibletube 7. Then, in the light source device, the image signal is subjectedto predetermined processing (such as signal processing, imageprocessing, and the like), and then the processed signal is sent to themonitor. In this way, an image (electronic image) taken by the imagingelement is displayed on the screen of the monitor.

In the above, the description was given for the case where a flexibletube for an endoscope according to the present invention is applied toan electronic endoscope (electronic type endoscope). However, it is tobe noted that a flexible tube of this invention may also be applied to afiberscope (optical type endoscope).

As shown in FIG. 2, the flexible tube 1A has a core body (structuralbody) 2 and an outer cover 3 that covers an outer periphery of the corebody 2. Further, inside the flexible tube 1A, there is formed a hollowspace 24 through which internal elements (such as optical fibers,cables, operation wires, tubular elements, and the like) can be passed.

The core body 2 acts as a reinforcing member for reinforcing theflexible tube 1A, and also acts as a protecting member for protectingthe internal elements described above. This core body 2 is constructedfrom a coil 21 and a reticular tube 22 which covers the outer peripheryof the coil 21, so that the core body 2 has an elongated tubular shape.By constructing the core body 2 using the coil 21 and the reticular tube22, it becomes possible to give the flexible tube 1 torque transmissionability, tracking ability to a body cavity (i.e., bendability), andsufficient mechanical strength.

The coil 21 is formed from a flat metal band. Specifically, this coil 21is formed by winding the metal band into a spiral form so as to have auniform diameter with a gap 25 between the adjacent windings. Preferredexamples of materials which may be used for the metal band includestainless steel, copper alloys, and the like.

The reticular tube 22 is formed by weaving a plurality of bundles offine metal wires 23 in a lattice manner so as to have spaces 26 therebetween as shown in FIG. 2. Each of the bundles is formed by arranging aplurality of fine wires side by side. This reticular tube 22 may beformed from nonmetal fibers. Preferred examples of materials which maybe used for the fine metal wires 23 include stainless steel, copperalloys and the like. In this invention, it is preferred that at leastone of the fine wires (or fibers) constituting the reticular tube 22 iscoated with a synthetic resin so that a coating of the synthetic resinis provided thereon.

On the outer periphery of the reticular tube 22, each of the spaces 26of the reticular tube 22 forms either a recess or hole of the core body2 depending on its location with respect to the coil 21. Specifically,as shown in FIG. 2, some of the spaces 26 located on the metal band ofthe coil 21 form recesses of the core body 2, while the other spaces 26located on the gaps 25 between the adjacent windings form holes of thecore body 2. As a result of the structure described above, the core body2 has a plurality of recesses and holes.

The outer periphery of the core body 2 is covered with the outer cover3. This outer cover 3 or a portion of the outer cover 3 is formed into alaminate structure which is composed of inner, outer and intermediatelayers 31–33.

As will be described below, one of the inner, outer and intermediatelayers 31–33 of the outer cover 3 is formed of a material which isdifferent from a material constituting one of the other layers in itsphysical property or chemical property. Examples of such physicalproperty include stiffness, flexibility, hardness, elongation rate,tensile strength, shearing strength, bending strength and the like.Further, examples of such chemical property include chemical resistance,weather resistance and the like.

(I-2) Inner Layer of Outer Cover

The inner layer 31 of the outer cover 3 is formed on the innermost sideof the outer cover 3, and it adheres to the core body 2. Physicalproperty of the inner layer 31 is substantially homogeneous over itsentire region.

On the inner peripheral surface of the inner layer 31, as shown in FIG.2, there are integrally formed a plurality of projections (anchoringprojections) 4. Respective projections 4 project into spaces 26 of thecore body 2 (i.e., holes and recesses of the core body 2). As shown inFIG. 2, in the recesses (spaces 26) of the core body 2, each of theprojections 4 extends to the outer periphery of the coil 21. Further, inthe holes (spaces 26) of the core body 2, each of the projections 4extends into the gap 25 of the coil 21.

In this invention, it is preferable that the inner layer 31 is made of amaterial by which formation of the projections 4 can be controlledappropriately, so that appropriate number of projections 4 havingappropriate size and shape can be integrally formed on the inner layer31 as shown in FIG. 2.

By forming the projections 4 as described above, engagements between theprojections 4 and the recesses of the core body 2 and between theprojections 4 and the holes of the core body 2 are achieved, andtherefore the outer cover 3 is firmly fixed with respect to the corebody 2 by anchoring effect given by the engagements. Such anchoringeffect enables the outer cover 3 to expand and contract sufficiently inconformity with the bending of the core body 2. Further, due to theanchoring effect, it is possible to maintain a state that the outercover 3 adheres to the core body 2 even when the flexible tube 1A isbended. Therefore, by forming the flexible tube in this way, it ispossible to give high flexibility to the flexible tube.

Further, the bonding strength between the outer cover 3 and thereticular tube 22 is enhanced by the formation of the projections 4, sothat the peeling off of the outer cover 3 from the reticular tube 22 isprevented even after repeated use of the endoscope. This means that theflexible tube 1A of this invention can maintain high flexibility evenafter the endoscope is repeatedly used, that is, the flexible tube hasexcellent durability.

Further, when the coating of the synthetic resin is given to at leastone of the fine wires 23 forming the reticular tube 22 as describedabove, at least a part of the applied coating (synthetic resin) is fusedwith and is bonded to the inner layer 31, thereby providing strongbonding therebetween. In this case, in order to enhance the bodingstrength between the fine wires 23 and the inner layer 31, it ispreferable that the inner layer 31 of the outer cover 3 contains amaterial that has a compatibility with the synthetic resin of thecoating.

By using the reticular tube 22 formed from the fine wires with thecoating of the synthetic resin as described above, a higher adhesionbetween the outer cover 3 and the core body 2 is realized. Therefore, byproviding the outer cover 3 on the core body 2 having the reticular tube22 with the coating of the synthetic resin and by forming theprojections 4 on the inner layer 31 as described above, it becomespossible to obtain a flexible tube having high flexibility and highdurability. In this connection, it is to be noted this excellent abilityis given by the effect of the coating of the synthetic resin provided onthe fine wire(s) as well as the effect of the projections 4 describedabove.

In this invention, a constituent material for the inner layer 31 is notparticularly limited. Examples of such material include various resinshaving elasticity such as polyvinyl chloride, polyolefine (e.g.,polyethylene, polypropylene, ethylene-vinylacetate copolymer and thelike), polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate and the like), polyurethane, polystyreneresin, fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer and the like), polyimide, and thelike; and various elastomers such as polyurethane-based elastomer,polyester-based elastomer, polyolefine-based elastomer, polyamide-basedelastomer, polystyrene-based elastomer, fluorine-based elastomer,silicone rubber, fluororubber, latex rubber, and the like. These can beused alone or as a mixture of two or more thereof. In this invention, amaterial containing at least one of polyurethane-based elastomer,polyolefin-based elastomer, and polyester-based elastomer is preferablyused to form the inner layer 31, since they can be easily formed intothe inner layer with the projections 4 as shown in FIG. 2.

The average thickness of the inner layer 31 (excluding the portions ofthe projections 4) is not particularly limited, but the thickness ispreferably in the range of 0.05 to 0.8 mm, and more preferably in therange of 0.05 to 0.4 mm.

(I-3) Outer Layer of Outer Cover

The outer layer 32 is formed on the outermost side of the outer cover 3,and has almost homogeneous physical properties over its entire region.In this invention, it is preferable that the outer layer 32 is formed ofa material having a resistance to chemicals. By using such a material,it is possible to suppress the degradation of the outer cover 3 due torepeated cleaning and disinfection. Further, it is also possible tosuppress deterioration in flexibility caused by the hardening of theouter cover due to repeated cleaning and disinfection. In addition, itis also possible to prevent peeling off of the outer cover 3 from thereticular tube 22 due to cracks or the like caused by repeated cleaningand disinfection.

The outer layer 32 is formed so as to have a relatively high hardness.This prevents the generation of scratches that are liable to producecracks or the like on the surface of the outer cover 3. In thisinvention, it is preferable that the outer layer 32 of the outer cover33 has higher hardness than that of any one of the inner andintermediate layers 31 and 33 in part or over its entire region.

In this invention, a constituent material for the outer layer 32 is notparticularly limited. Examples of such material include various resinshaving elasticity such as polyvinyl chloride, polyolefine (e.g.,polyethylene, polypropylene, ethylene-vinylacetate copolymer and thelike), polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate and the like), polyurethane, polystyreneresin, fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer and the like), polyimide, and thelike; and various elastomers such as polyurethane-based elastomer,polyester-based elastomer, polyolefine-based elastomer, polyamide-basedelastomer, polystyrene-based elastomer, fluorine-based elastomer,silicone rubber, fluororubber, latex rubber, and the like. These can beused alone or as a mixture of two or more thereof. In this invention, amaterial containing at least one of polyolefine (e.g.,ethylene-vinylacetate copolymer and the like), fluoro-based resin (e.g.,polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer and thelike), polyester-based elastomer, polyolefine-based elastomer,fluorine-based elastomer, silicone rubber and fluororubber is preferablyused to form the outer layer 32, since they have high resistance tochemical.

The thickness of the outer layer 32 is not particularly limited, but thethickness is preferably in the range of 0.05 to 0.8 mm, and morepreferably in the range of 0.05 to 0.4 mm.

(I-4) Intermediate Layer of Outer Cover

In this invention, it is preferable that the intermediate layer 33 has ahigher elasticity than that of the outer layer 32, and more preferablythe intermediate layer 33 has a higher elasticity than that of any oneof the inner and outer layers 31 and 32. With this arrangement, theintermediate layer 33 functions as a cushioning layer (cushioning means)between the inner layer 31 and the outer layer 32. (In the following,such a function of the intermediate layer 33 is referred to as“cushioning function.”) Accordingly, by forming the intermediate layer33 as described above, it is possible to give higher flexibility to theflexible tube.

Hereinafter, the cushioning function of the intermediate layer 33 isdescribed in more detail. When the flexible tube 1A is bent by anexternal force, the high elastic force is generated in the bentintermediate layer 33 through the deformation thereof. The generatedelastic force is transmitted effectively to the inner layer 31 and theouter layer 32, respectively, since the intermediate layer 33 issandwiched between the inner layer 31 and the outer layer 32 each ofwhich has relatively low elasticity. When the external force has beenremoved, the bent flexible tube 1A is restored to its original shape bythe high elastic force generated in the bent intermediate layer 33. Inthis connection, it is to be noted that the restoration of the flexibletube into its original shape is achieved by the cushioning function ofthe intermediate layer 33, and that such a cushioning function gives theflexible tube high flexibility.

In this invention, a constituent material for the intermediate layer 33is not particularly limited. Examples of such material include variousresins having elasticity such as polyvinyl chloride, polyolefine (e.g.,polyethylene, polypropylene, ethylene-vinylacetate copolymer),polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate), polyurethane, polystyrene resin,fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer), polyimide, and the like; andvarious elastomers such as polyurethane-based elastomer, polyester-basedelastomer, polyolefine-based elastomer, polyamide-based elastomer,polystyrene-based elastomer, fluorine-based elastomer, silicone rubber,fluororubber, latex rubber, and the like. These can be used alone or asa mixture of two or more thereof. In this invention, a materialcontaining at least one of low hardness polyurethane-based elastomer,low hardness polyolefin-based elastomer, and low hardnesspolyester-based elastomer is preferably used to form the intermediatelayer 33, since such elastomers have high elasticity.

Although the intermediate layer 33 in this embodiment is given a singlelayer structure, it may be given a structure of two or more layers.

The average thickness of the intermediate layer 33 is not particularlylimited, but the average thickness is preferably in the range of 0.05 to0.8 mm, and more preferably in the range of 0.05 to 0.4 mm.

(I-5) Outer Cover Having the Layers

In this invention, the average thickness of the outer cover 3 (excludingthe portions of the projections 4) is not particularly limited, as longas the outer cover 3 can protect the core body 2 and the internalelements arranged in the core body 2 from a fluid (e.g., body fluid) andit does not impair the bendability of the flexible tube. However, theaverage thickness of the outer cover 3 (excluding the portions of theprojections 4) is preferably in the range of 0.15 to 0.9 mm, and morepreferably in the range of 0.3 to 0.8 mm.

In addition, it is preferable that the outer cover 3 (excluding theportions of the projections 4) has a substantially uniform-thicknessover its entire region. With this arrangement, it is possible to producea flexible tube having a substantially uniform diameter over its entireregion. When an endoscope having a flexible tube with such an outercover is used in an endoscopic examination, it is possible for anoperator to easily and smoothly insert the insertion section (flexibletube) of the endoscope into a body cavity of a patient, thus making itpossible to reduce the burden on the patient during the endoscopicexamination.

(I-6) Manufacturing Method of Flexible Tube

A method of manufacturing a flexible tube for an endoscope as describedin the above is not particularly limited, but it is preferable that theflexible tube of this invention is manufactured by extrusion molding.When such extrusion molding is performed using an extrusion moldingmachine equipped with a plurality of extrusion ports, it is possible toextrude the inner, outer and intermediate layers 31–33 simultaneously sothat the core body 2 is covered with the outer cover 3 having thelaminate structure composed of these layers. In this extrusion molding,it is preferable to adjust the feeding amount (i.e., feeding amount perunit time) of constituent material for each layer from each extrusionport while adjusting the feeding speed of the core body 2. This methodmakes it is possible to control properly the thickness, shape andproperty of each layer.

The temperature of the material when performing the extrusion molding isnot particularly limited, but the temperature is preferably about 130 to220° C., and more preferably about 165 to 205° C. Within such a range,the material has an excellent moldability. Therefore, by performing theextrusion molding using the material whose temperature is within therange described above, it becomes possible to improve uniformity of thethickness of the outer cover 3 provided on the core body 2.

II. EXAMPLES OF FIRST EMBODIMENT

Next, specific examples of the first embodiment of the present inventionwill be described below.

1. Preparation of Flexible Tube for an Endoscope

Example 1a

First, a coil 21 having an outer diameter of 9.9 mm and an innerdiameter of 9.6 mm was prepared by winding a band-shaped stainless steelmaterial having a width of 3 mm. Next, stainless steel fine wires 23 atleast one of which had been given a coating of a polyamide resin andeach of which had a diameter of 0.1 mm were prepared, and then usingthese fine wires a plurality of bundles of ten fine wires were prepared.These bundles of the ten fine wires 23 were woven together in a latticemanner to obtain a reticular tube 22. Then, the obtained reticular tube22 was provided on the prepared coil 21 so that the outer periphery ofthe coil 21 was covered with the reticular tube 22. In this way, a corebody 2 was prepared.

Next, using an extrusion-molding machine, an outer cover 3 composed ofinner, outer and intermediate layers 31–33 was provided on the outerperiphery of the core body 2 so that the core body 2 was covered withthe outer cover 3. In this way, a flexible tube for an endoscope with alength of 1.6 m was prepared. In this connection, it is to be noted thatthe length of 1.6 m means the length of an available (effective) portionof the flexible tube that can be used for a flexible tube for anendoscope, that is the length of 1.6 m means an available (effective)length of the flexible tube. Therefore, the actually prepared flexibletube had a length more than 1.6 m by including additional portions atthe both ends of the available portion of the flexible tube. In thisregard, however, it goes without saying that the available length is notlimited to 1.6 m mentioned above.

A constituent material used for each of the layers in this Example isshown in the attached Table 1. In addition, the thickness of each of thelayers is also shown in Table 1.

Example 1b

A flexible tube for an endoscope was prepared in the same manner as inExample 1a except that the thickness of the inner layer 31 was changedas shown in the attached Table 1.

Example 1c

A flexible tube for an endoscope was prepared in the same manner as inExample 1a except that the thickness of the intermediate layer 33 waschanged as shown in the attached Table 1.

Example 1d

A flexible tube for an endoscope was prepared in the same manner as inExample 1a except that the thickness of the outer layer 32 and thematerial for the outer layer 32 were changed as shown in the attachedTable 1.

Example 1e

A flexible tube for an endoscope was prepared in the same manner as inExample 1a except that the material for the outer layer 32 was changedas shown in the attached Table 1.

Comparative Example 1a

A core body 2 was prepared in the same manner as in Example 1a. Then,using an extrusion-molding machine, an outer cover 3 composed of innerand outer layers 31 and 32 was provided on the outer periphery of thecore body 2 so that the core body 2 was covered with the outer cover 3.In this way, a flexible tube for an endoscope with a length of 1.6 m wasprepared. A constituent material for each layer of the outer cover 3 andthe thickness of each layer are shown in the attached Table 1.

Comparative Example 1b

A flexible tube for an endoscope was prepared in the same manner as inComparative Example 1a except that the material for the outer layer 32was changed as shown in the attached Table 1.

Comparative Example 1c

A flexible tube for an endoscope was prepared in the same manner as inExample 1a except that the thickness of each of inner and outer layers31 and 32 and the material for each of the inner and outer layers 31 and32 were changed as shown in the attached Table 1.

Comparative Example 1d

A flexible tube for an endoscope was prepared in the same manner as inExample 1a except that the material for each of inner and outer layers31 and 32 was changed as shown in the attached Table 1.

2. Observation of the Prepared Flexible Tubes

An observation of the cross-section of the outer cover was carried outfor each of the flexible tubes of Examples 1a–1e and ComparativeExamples 1a–1d. Through the observation, formation of projections 4 asshown in FIG. 2 was observed in each of the flexible tubes of Examples1a–1e and Comparative Examples 1a, 1b and 1d, but no formation ofprojections 4 was observed in the flexible tube of Comparative Example1c.

3. Evaluation of Flexible Tube

(3-1) Chemical Resistance Test

A chemical resistance test was carried out for each of the flexibletubes of Example 1a–1e and Comparative Example 1a–1d. In this test, 100L of 10% aqueous solution of iodine held at 25° C. was prepared first,and then each of the prepared flexible tubes was immersed in the aqueoussolution for 200 hours. Then, the condition of each flexible tube wasevaluated in accordance with the four rankings A–D given below.

-   Rank A:    -   No Change in the Appearance; and    -   No Occurrence of Cracks and Blisters in Outer Cover.-   Rank B:    -   Slight Change in the Appearance; and    -   Occurrence of Blisters at a Few Spots of Outer Cover.-   Rank C:    -   Large Change in the Appearance; and    -   Occurrence of Blisters at Many Spots of Outer Cover.-   Rank D:    -   Extremely Large Change in the Appearance; and    -   Occurrence of a Large Number of Cracks and Blisters on Outer        Cover.

The evaluation results in this test are shown in the attached Table 1.

(3-2) Flexibility Test

A flexibility test was carried out for each of the flexible tubes ofExample 1a–1e and Comparative Example 1a–1d. In this test, the flexibletube for an endoscope supported at its both ends was subjected tobending by 90°, and the flexibility in that state was evaluated inaccordance with the four rankings A–D given below.

-   Rank A:    -   High Flexibility    -   (A flexible tube of Rank A is considered to be best suited for        use as a flexible tube for an endoscope.)-   Rank B:    -   Normal Flexibility    -   (A flexible tube of Rank B is considered to be suited for use as        a flexible tube for an endoscope.)-   Rank C:    -   Low Flexibility    -   (A flexible tube of Rank C is considered to have problems in use        as a flexible tube for an endoscope.)-   Rank D:    -   Almost No Flexibility    -   (A flexible tube of Rank D is considered to be unsuited for use        as a flexible tube for an endoscope.)

The result of the flexibility test is shown in the attached Table 1.

(3-3) Durability Test

A durability test was carried out for each of the flexible tubes ofExamples 1a–1e and Comparative Examples 1a–1d. In the durability test,each of the flexible tubes was set to a state where the flexible tubewas supported at its both ends, and in this state the operation ofbending by 90° was repeated 300 times. Then, the degree of change in theflexibility after the repeated operation of bending was examined toevaluate the durability of each flexible tube in accordance with thefour rankings A–D given below.

-   Rank A:    -   Almost No Change in Flexibility    -   (A flexible tube of Rank A is considered to have extremely high        durability.)-   Rank B:    -   Slight Lowering of Flexibility (A flexible tube of Rank B is        considered to have high durability.)-   Rank C:    -   Large Lowering of Flexibility (A flexible tube of Rank C is        considered to have problems    -   in its durability.)-   Rank D:    -   Extremely Large Lowering of Flexibility; and    -   Occurrence of cracks and the like at many spots of the outer        cover.    -   (A flexible tube of Rank D is considered to be unsuited for use        as a flexible tube for an endoscope.)

The result of the durability test is shown in the attached Table 1.

(3-4) Evaluation

The results in the attached Table 1 show that the flexible tubeaccording to the present invention (i.e., Examples 1a –1e) has highchemical resistance and high flexibility as well as high durability.Further, the results in Table 1 also show that conventional flexibletubes (i.e., Comparative Examples 1a–1d) have some drawbacks.

Specifically, the flexible tube of Comparative Example 1a has poorresistance to chemical. This drawback is considered to result from thefact that the outer layer 32 of the outer cover 3 was made of thematerial with poor chemical resistance. Further, the flexible tube ofComparative Example 1b has poor flexibility. This drawback is consideredto result from the fact that both the inner and outer layers 31 and 32were formed of the materials with relatively high hardness. Furthermore,the flexible tube of Comparative Example 1c has poor flexibility andpoor durability. These drawbacks are considered to result from the factthat no projections 4 as shown in FIG. 2 were formed on the inner layer31. In addition, the flexible tube of Comparative Example 1d has poordurability. This drawback is considered to result from the fact that theinner layer 31 was formed of the material with relatively low hardnessand therefore the projections 4 on the inner layer 31 had poor strength.

According to the present invention described above, appropriatematerials that are suitable for each of layers of an outer cover 3 areused for preparing an outer cover 3, and the outer cover 3 is providedonto the core body 2 so that each of the layers has appropriatethickness and shape. This structure and the selection of material makeit possible to provide a flexible tube for an endoscope that has highdurability and high flexibility as well as high chemical resistance.

Further, when a material with high elasticity is used for theintermediate layer of the outer cover, it is possible to give higherflexibility to the flexible tube. In addition, when a material having ahigh adhesion with the core body is used for the inner layer of theouter cover, it is also possible to give high durability to the flexibletube for an endoscope.

III. Second Embodiment (Flexible Tube 1B)

Next, a second embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 3. FIG. 3 is a sectional view whichshows a part of a flexible tube 1B according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1. Inthe following, description of the configurations and features that arethe same as those in the above-mentioned first embodiment will beomitted, and description will be given mainly with respect to theconfigurations and features that are different from those of the firstembodiment.

As shown in FIG. 3, an outer cover (or a portion of the outer cover) 3of the flexible tube 1B has a laminate structure which is composed ofinner, outer and intermediate layers 31–33. The inner layer 31 has asmaller thickness at a portion nearer to the tip end 12 of the flexibletube 1B, while each of the outer and inner layers 32 and 33 has asubstantially uniform thickness over its entire region. This structuregives the outer cover 3 a stiffness (e.g., bending stiffness) thatdecreases in the longitudinal direction from the base end 11 toward thetip end 12. By forming the outer cover 3 such that its stiffness variesin the longitudinal direction, it is possible to give a flexible tubeflexibility that increases in the longitudinal direction from the baseend 11 toward the tip end 12. According to such a flexible tube for anendoscope, since the flexible tube has a higher stiffness in a portioncloser to the base end 11, it is possible to fully transmit to the tipend 12 the push-in force and the rotational force applied by theoperator. On the other hand, since the flexible tube has highflexibility in a portion closer to the tip end 12, it is also possibleto smoothly insert an insertion section (flexible tube) of an endoscopeinto an internal curved portion of a patient in a safe manner.Therefore, the flexible tube 1B as described above makes it possible foran operator to insert the insertion section with easy manipulation, thusenabling the reduction of the burden on the patient during theendoscopic examination.

In this embodiment, the rate of change in the thickness of the innerlayer 31 in the longitudinal direction, that is, the shape of the innerlayer 31 is appropriately determined to realize the desired rate ofchange in the stiffness of the flexible tube in the longitudinaldirection. This makes it possible, for example, to produce various kindsof flexible tubes for an endoscope taking into account various shapes ofinternal portions of a living body, operator's tastes and the like.

Further, in this embodiment, the value of T1 _(min)/T1 _(max) is notparticularly limited, where the value of “T1 _(min)” is given by thethickness of the thinnest part of the inner layer 31, and the value of“T1 _(max)” is given by the thickness of the thickest part of the innerlayer 31. However, the value of T1 _(min)/T1 _(max) is preferably in therange of 0.05 to 0.95, and more preferably in the range of 0.1 to 0.6.

IV. Third Embodiment (Flexible Tube 1C)

Next, a third embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 4. FIG. 4 is a sectional view whichshows a part of a flexible tube 1C according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.

In this embodiment, an outer cover 3 of the flexible tube 1C has alaminate structure composed of inner, outer and intermediate layers31–33. Each of the inner and intermediate layers 31 and 33 has athickness which gradually varies over its entire region; and the outerlayer 32 has a substantially uniform thickness over its entire region.

As shown in FIG. 4, the thickness of the inner layer 31 gradually“decreases” in the direction from the base end 11 toward the tip end 12.Conversely, the thickness of the intermediate layer 33 gradually“increases” in the direction from the base end 11 toward the tip end 12.In this embodiment, the intermediate layer 33 is formed of a materialhaving higher elasticity than that of the inner layer 31.

In this connection, it is to be noted that the thickness of theintermediate layer 33 decreases in the opposite direction to that of theinner layer 31. Further, it is also to be noted that the total thicknessof the inner and intermediate layers 31 and 33 remains substantiallyuniform over the entire region of the outer cover 3, and the thicknessof the outer cover 3 remains substantially uniform over its entireregion, in spite of the fact that the thickness of each of the inner andintermediate layers 31 and 33 varies over its entire region.

In this embodiment, the value of T3 _(min)/T3 _(max) is not particularlylimited, where the value of “T3 _(min)” is given by the thickness of thethinnest part of the intermediate layer 33, and the value of “T3 _(max)”is given by the thickness of the thickest part of the intermediate layer33. However, the value of T3 _(min)/T3 _(max) is preferably in the rangeof 0.05 to 0.95, and more preferably in the range of 0.1 to 0.6.

According to the flexible tube 1C having the structure described above,in spite of the fact that the total thickness of the outer cover 3(excluding the portions of the projections 4) is substantially uniformover its entire region, the ratio of the thickness of the intermediatelayer 33 to that of each of the inner and outer layer 31 and 32 becomeslarger at a portion closer to the tip end 12. This structure makes itpossible for the flexible tube 1C to have higher stiffness againsttension and bending at a portion closer to the “base” end 11, and tohave higher flexibility at a portion closer to the “tip” end 12. Inother words, this structure makes it possible for the flexible tube 1Cto have flexibility which gradually varies in the longitudinaldirection.

According to the flexible tube for an endoscope as described above,since the flexible tube has higher stiffness in a portion closer to thebase end 11, it is possible to fully transmit to the tip end 12 thepush-in force and the rotational force applied by the operator. On theother hand, the flexible tube has higher flexibility in a portion closerto the tip end 12, it is also possible to smoothly insert an insertionsection (flexible tube) of an endoscope into an internal curved portionof a patient in a safe manner. Therefore, the flexible tube as describedabove makes it possible for an operator to insert the insertion sectionwith easy manipulation, thus enabling the reduction of the burden on thepatient during the endoscopic examination.

Further, according the flexible tube 1C of this embodiment, the outercover 3 is formed such that the thickness of one of the inner andintermediate layers 31 and 33 decreases in the opposite direction to theother layer. This results in that the flexible tube 1C has a uniformouter diameter over its entire region. When such a flexible tube havinga uniform outer diameter is actually used, it is possible to reduce theburden on the patient during endoscopic examination.

V. Fourth Embodiment (Flexible Tube 1D)

Next, a fourth embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 5. FIG. 5 is a sectional view whichshows a part of a flexible tube 1D according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1. (i.e., side closer to an operator), and theleft-hand side corresponds, to the side of tip end 12 shown in FIG. 1.Further, in this figure, the reference numeral “I” indicates a regionwhere a thickness-varying region is formed, and each of the referencenumerals “II” and “III” indicates a region where no thickness-varyingregion is formed. (In this description, a region within which thethickness of a layer increases or decreases is referred to as a“thickness-varying region” of the layer.) In this connection, it is tobe noted that the total length of the regions I, II and III correspondsto the length of an outer cover 3 of the flexible tube 1D.

As shown in FIG. 5, the outer cover 3 of the flexible tube 1D has alaminate structure composed of inner, outer and intermediate layers31–33. Each of the inner and intermediate layers 31 and 33 has athickness-varying region 34 within the region I, and the outer layer 32has a substantially uniform thickness over its entire region. Thethickness-varying region of each of the inner and intermediate layers 31and 33 has a relatively small length (e.g., approximately 5 to 80 mm).In this embodiment, the intermediate layer 33 is formed of a materialhaving higher elasticity than that of the inner layer 31.

The thickness-varying region 34 of the inner layer 31 is formed at aspecific portion of this layer (i.e., within the region I), and as shownin FIG. 5 the thickness of this thickness-varying region 34 graduallydecreases within the region I in the direction from the base end 11toward the tip end 12. Within the regions II and III the inner layer 31has a substantially uniform thickness, but it has larger thicknesswithin the region III as compared with the thickness within the regionII.

Similarly the thickness-varying region 34 of the intermediate layer 33is also formed within the region I, and as shown in FIG. 5 the thicknessof this thickness-varying region 34 gradually decreases within theregion I in the direction from the tip end 12 toward the base end 11(i.e., in the direction opposite to that of the thickness-varying region34 of the inner layer 31). Within the regions II and III theintermediate layer 32 has a substantially uniform thickness, but it haslarger thickness within the region II as compared with the thicknesswithin the region III.

It is to be noted that in this embodiment the outer cover 3 having theinner, outer and intermediate layers 31–33 is formed so that thethickness-varying regions 34 of the inner and intermediate layers 31 and33 face (overlap) each other in the thickness direction as shown in FIG.5. Further, it is also to be noted that the total thickness of the innerand intermediate layers 31 and 33 remains substantially uniform over theentire region of the flexible tube 1D in spite of the fact that theselayers have a thickness-varying region.

According to the flexible tube 1D having the structure described above,since the intermediate layer 33 is formed of a material having higherelasticity than that of the inner layer 31, the outer cover 3 has arelatively high stiffness (low flexibility) within the region III, whileit has a relatively low stiffness (high flexibility) within the regionII. In addition, the outer cover 3 has a medium stiffness within theregion I where the thickness-varying regions 34 are formed, and thestiffness of this portion varies in the longitudinal direction. Thestructure described above gives higher stiffness to the base side region(region III) of the flexible tube 1D, while it gives higher flexibilityto the tip side region (region II) of the flexible tube 1D. In addition,the structure described above makes it possible to form a flexible tubesuch that its stiffness (flexibility) varies gradually or stepwisewithin a portion where a thickness-varying region(s) is formed.According to such a flexible tube, since it has higher stiffness in aportion closer to the base end 11, it is possible to fully transmit tothe tip end 12 the push-in force and the rotational force applied by theoperator. On the other hand, the flexible tube has high flexibility in aportion closer to the tip end 12, it is also possible to smoothly insertan insertion section (flexible tube) of an endoscope into an internalcurved portion of a patient in a safe manner. Therefore, the flexibletube as described above makes it possible for an operator to insert theinsertion section with easy manipulation, thus enabling the reduction ofthe burden on the patient during the endoscopic examination.

Further, according the flexible tube 1D in this embodiment, the flexibletube 1D has a uniform outer diameter over its entire region in spite ofthe fact that each of the inner and intermediate layers 31 and 33 has athickness-varying region 34. Therefore, when such a flexible tube havinga uniform outer diameter is used, it is possible to reduce the burden onthe patient during endoscopic examination.

VI. Fifth Embodiment (Flexible Tube 1E)

Next, a fifth embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 6. FIG. 6 is a sectional view whichshows a part of a flexible tube 1E according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.

In this embodiment, an outer cover 3 of the flexible tube 1E has alaminate structure composed of inner, outer and intermediate layers31–33. The inner layer 31 has a substantially uniform thickness over itsentire region. The thickness of each of the outer and intermediatelayers 32 and 33 varies over the entire region. As shown in FIG. 6, thethickness of the outer layer 32 gradually “decreases” in the directionfrom the base end 11 toward the tip end 12. Conversely, the thickness ofthe intermediate layer 33 gradually “increases” in the direction fromthe base end 11 toward the tip end 12. In this embodiment, theintermediate layer 33 is formed of a material having higher elasticitythan that of the outer inner layer 31.

In this connection, it is to be noted that the thickness of theintermediate layer 33 decreases in the opposite direction to that of theouter layer 32. Further, it is also to be noted that the total thicknessof the outer and intermediate layers 32 and 33 remains substantiallyuniform over the entire region of the flexible tube 1E, and thethickness of the outer cover 3 remains substantially uniform over itsentire region in spite of the fact that the thickness of each of theouter and intermediate layers 32 and 33 varies over its entire region.

In this embodiment, the value of T2 _(min)/T2 _(max) is not particularlylimited, where the value of “T2 _(min)” is given by the thickness of thethinnest part of the outer layer 32, and the value of “T2 _(max)” isgiven by the thickness of the thickest part of the outer layer 32.However, the value of T2 _(min)/T2 _(max) is preferably in the range of0.05 to 0.95, and more preferably in the range of 0.1 to 0.6.

According to the flexible tube 1E of this invention, it is possible toachieve the same advantages as those described with respect to theflexible tube 1C (FIG. 4) in the third embodiment.

VII. Sixth Embodiment (Flexible Tube 1F)

Next, a sixth embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 7. FIG. 7 is a sectional view whichshows a part of a flexible tube 1F according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.Further, in this figure, the reference numeral “I” indicates a regionwhere a thickness-varying region is formed, and each of the referencenumerals “II” and “III” indicates a region where no thickness-varyingregion is formed. In this connection, it is to be noted that the totallength of the regions I, II and III corresponds to the length of anouter cover 3 of the flexible tube 1F.

As shown in FIG. 7, the outer cover 3 of the flexible tube 1F has alaminate structure composed of inner, outer and intermediate layers31–33. Each of the outer and intermediate layer 32 and 33 has athickness-varying region 34 within the region I, and the inner layer 31has a substantially uniform thickness over its entire region. Thethickness-varying region 34 of each of the outer and intermediate layers32 and 33 has relatively small length (e.g., approximately 5 to 80 mm).In this embodiment, the intermediate layer 33 is formed of a materialhaving higher elasticity than that of the outer layer 32.

The thickness-varying region 34 of the outer layer 32 is formed at aspecific portion of this layer (i.e., within the region I), and as shownin FIG. 7 the thickness of this thickness-varying region 34 graduallydecreases within the region I in the direction from the base end 11toward the tip end 12. Within the regions II and III the outer layer 32has a substantially uniform thickness, but it has larger thicknesswithin the region III as compared with the thickness within the regionII.

Similarly the thickness-varying region 34 of the intermediate layer 33is also formed within the region I, but as shown in FIG. 7 the thicknessof this thickness-varying region 34 gradually decreases within theregion I in the direction from the tip end 12 toward the tip end 12(i.e., in the direction opposite to that of the thickness-varying region34 of the outer layer 32). Within the regions II and III theintermediate layer 33 has a substantially uniform thickness, but it haslarger thickness within the region II as compared with the thicknesswithin the region III.

It is to be noted that in this embodiment the outer cover 3 having theinner, outer and intermediate layers 31–33 is formed so that thethickness-varying regions 34 of the outer and intermediate layers 32 and33 face (overlap) each other in the thickness direction as shown in FIG.7. Further, it is also to be noted that the total thickness of the outerand intermediate layers 32 and 33 remains substantially uniform over theentire region of the outer cover 3 in spite of the fact that each of theouter and intermediate layers 32 and 33 has a thickness-varying region.

According to the flexible tube 1F of this invention, it is possible toachieve the same advantages as those described with respect to theflexible tube 1D in the fourth embodiment.

VIII. Examples of Second–Sixth Embodiments

Next, specific examples of the second–sixth embodiments described abovewill be described below.

1. Preparation of Flexible Tube for an Endoscope

Example 2a

First, a coil 21 having an outer diameter of 9.9 mm and an innerdiameter of 9.6 mm was prepared by winding a band-shaped stainless steelmaterial having a width of 3 mm. Next, stainless steel fine wires 23 atleast one of which had been given a coating of a polyamide resin andeach of which had a diameter of 0.1 mm were prepared, and then usingthese fine wires a plurality of bundles of ten fine wires were prepared.These bundles of the ten fine wires 23 were woven together in a latticemanner to obtain a reticular tube 22. Then, the obtained reticular tube22 was provided on the prepared coil 21 so that the outer periphery ofthe coil 21 was covered with the reticular tube 22. In this way, a corebody 2 was prepared.

Next, using an extrusion-molding machine, an outer cover 3 composed ofinner, outer and intermediate layers 31–33 was provided on the outerperiphery of the core body 2 so that the core body 2 was covered withthe outer cover 3. (A constituent material used for each of the layersin this Example is as shown in the attached Table 2.) In this way, aflexible tube for an endoscope with a length of 1.6 m was prepared. Inthis connection, it is to be noted that the length of 1.6 m means thelength of an available (effective) portion of the flexible tube that canbe used for a flexible tube for an endoscope, that is the length of 1.6m means an available (effective) length of the flexible tube. Therefore,the actually prepared flexible tube had a length more than 1.6 m byincluding additional portions at the both ends of the available portionof the flexible tube (See FIG. 13). In this regard, however, it goeswithout saying that the available length is not limited to 1.6 mmentioned above.

In the preparation described above, the outer cover 3 was provided overthe core body 2 such that the thickness of the inner layer 31 graduallyincreases at a constant rate between both ends 11 and 12 of the flexibletube in the direction from the tip end 12 toward base end 11.Specifically, the inner layer 31 was formed over the entire region(length) of the outer cover 3 so as to have a thickness of 0.05 mm (T1_(min)) at the tip end 12 and have a thickness of 0.44 mm (T1 _(max)) atthe base end 11. In the inner layer 31 of the prepared flexible tube,the T1 _(min)/T1 _(max) had a value of 0.125, where the value of “T1_(min)” is given by the thickness of the thinnest part of the innerlayer 31, and the value of “T1 _(max)” is given by the thickness of thethickest part of the inner layer 31.

In addition, the intermediate layer 33 was formed such that itsthickness gradually decreases at a constant rate between the both ends11 and 12 in the direction from the tip end 12 toward base end 11.Specifically, the intermediate layer 33 was formed over the entireregion (length) of the outer cover 3 so as to have a thickness of 0.05mm (T3 _(min)) at the base end 11 and have a thickness of 0.4 mm (T3_(max)) at the tip end 12. In the intermediate layer 33 of the preparedflexible tube, the T3 _(min)/T3 _(max) had a value of 0.125, where thevalue of “T3 _(min)” is given by the thickness of the thinnest part ofthe intermediate layer 33, and the value of “T3 _(max)” is given by thethickness of the thickest part of the intermediate layer 33.

The outer layer 32 of the outer cover 3 was formed over the entireregion (length) of the outer cover 3 so as to have a uniform thickness(0.1 mm).

Example 2b

A flexible tube for an endoscope was prepared in the same manner as inExample 2a except that the thickness (shape) of each layer of an outercover 3 was changed as follows.

In the preparation of the flexible tube, the outer cover 3 was providedover the core body 2 such that the thickness of the outer layer 32gradually increases at a constant rate between both ends 11 and 12 ofthe flexible tube in the direction from the tip end 12 toward base end11. Specifically, the outer layer 32 was formed over the entire region(length) of the outer cover 3 so as to have a thickness of 0.05 mm (T2_(min)) at the tip end 12 and have a thickness of 0.4 mm (T2 _(max)) atthe base end 11. In the inner layer 31 of the prepared flexible tube,the T2 _(min)/T2 _(max) had a value of 0.125, where the value of “T2_(min)” is given by the thickness of the thinnest part of the outerlayer 32, and the value of “T2 _(max)” is given by the thickness of thethickest part of the outer layer 32.

In addition, the intermediate layer 33 was formed such that itsthickness gradually decreases at a constant rate between the both ends11 and 12 in the direction from the tip end 12 toward base end 11.Specifically, the intermediate layer 33 was formed over the entireregion (length) of the outer cover 3 so as to have a thickness of 0.05mm (T3 _(min)) at the base end 11 and have a thickness of 0.4 mm (T3_(max)) at the tip end 12. In the intermediate layer 33 of the preparedflexible tube, the T3 _(min)/T3 _(max) had a value of 0.125, where thevalue of “T3 _(min)” is given by the thickness of the thinnest part ofthe intermediate layer 33, and the value of “T3 _(max)” is given by thethickness of the thickest part of the intermediate layer 33.

The inner layer 31 of the outer cover 3 was formed over the entireregion (length) of the outer cover 3 so as to have a uniform thickness(0.1 mm).

Example 2c

A flexible tube for an endoscope was prepared in the same manner as inExample 2a except that the thickness (shape) of each layer of an outercover 3 was changed as follows.

In the preparation of the flexible tube, the outer layer 32 of the outercover 3 was formed such that its thickness increases stepwise in foursteps in the direction from the tip end 12 to the base end 11.Specifically, the outer layer 32 was formed over the entire region(length) of the outer cover 3 so as to have a thickness of 0.05 mm at afirst quarter (that is closest to the tip end 12) of the entire region;have a thickness of 0.15 mm at a second quarter adjacent to the firstquarter; have a thickness of 0.25 mm at a third quarter adjacent to thesecond quarter; and have a thickness of 0.4 mm at a fourth quarter (thatis closest to the base end 11) adjacent to the third quarter. In thisouter layer 32, the tip end 12 had a thickness of 0.05 mm (T2 _(min)),and the base end 11 had a thickness of 0.4 mm (T2 _(max)). Thus, the T2_(min)/T2 _(max) had a value of 0.125, where the value of “T2 _(min)”was given by the thickness of the thinnest part of the outer layer 32,and the value of “T2 _(max)” was given by the thickness of the thickestpart of the outer layer 32.

Further, the intermediate layer 33 of the outer cover 3 was formed suchthat the thickness decreases stepwise in four steps in the directionfrom the tip end 12 to the base end 11. Specifically, the intermediatelayer 33 had been formed over the entire region (length) of the outercover 3 so as to have a thickness of 0.4 mm at a first quarter (that isclosest to the tip end 12) of the entire region; have a thickness of0.25 mm at a second quarter adjacent to the first quarter; have athickness of 0.15 mm at a third quarter adjacent to the second quarter;and have a thickness of 0.05 mm at a fourth quarter (that is closest tothe base end 11) adjacent to the third quarter. In this intermediatelayer 33, the tip end 12 had a thickness of 0.05 mm (T3 _(min)), and thebase end 11 had a thickness of 0.44 mm (T3 _(max)). Thus, the T3_(min)/T3 _(max) had a value of 0.125, where the value of “T3 _(min)”was given by the thickness of the thinnest part of the intermediatelayer 33, and the value of “T3 _(max)” was given by the thickness of thethickest part of the intermediate layer 33.

In addition, the inner layer 31 of the outer cover 3 was formed over theentire region (length) of the outer cover 3 so as to have a uniformthickness (0.1 mm).

Example 2d

A flexible tube for an endoscope was prepared in the same manner as inExample 2b except that the thickness (shape) of an outer layer 32 of anouter cover 3 was changed as follows, and a constituent material for theouter layer 32 was changed as shown in the attached Table 2.

In the preparation of the flexible tube, the outer cover 3 was providedover the core body 2 such that the thickness of the outer layer 32gradually increases at a constant rate between the both ends 11 and 12of the flexible tube in the direction from the tip end 12 toward baseend 11. Specifically, the outer layer 32 was formed over the entireregion (length) of the outer cover 3 so as to have a thickness of 0.1 mm(T2 _(min)) at the tip end 12 and have a thickness of 0.45 mm (T2_(max)) at the base end 11. In the outer layer 32 of the preparedflexible tube, the T2 _(min)/T2 _(max) had a value of 0.222, where thevalue of “T2 _(min)” was given by the thickness of the thinnest part ofthe outer layer 32, and the value of “T2 _(max)” was given by thethickness of the thickest part of the outer layer 32.

Example 2e

A flexible tube for an endoscope was prepared in the same manner as inExample 2a except that a material for an outer layer 32 of an outercover 3 was changed as shown in the attached Table 2.

Comparative Example 2a

A core body 2 was prepared in the same manner as in Example 2a. Then,using an extrusion-molding machine, an outer cover 3 composed of twolayers (i.e., inner and outer layers 31 and 32) was provided on theouter periphery of the core body 2 so that the core body 2 was coveredwith the outer cover 3. In this way, a flexible tube for an endoscopewith a length of 1.6 m was prepared. A constituent material for eachlayer of the outer cover 3 is shown in the attached Table 2.

In the preparation of the flexible tube in this embodiment, the innerlayer 31 of the outer cover 3 was formed over the entire region (length)of the outer cover 3 so as to have a uniform thickness (0.2 mm).Further, the outer layer 32 of the outer cover 3 was formed over theentire region (length) of the outer cover 3 so as to have a uniformthickness (0.3 mm).

Comparative Example 2b

A flexible tube for an endoscope was prepared in the same manner as inComparative Example 2a except that a material for an outer layer 32 waschanged as shown in the attached Table 2.

Comparative Example 2c

A flexible tube for an endoscope was prepared in the same manner as inComparative Example 2a except that a material for each of inner andouter layers 31 and 32 was changed as shown in the attached Table 2.

2. Observation of the Prepared Flexible Tubes

An observation of the cross-section of the outer cover 3 was carried outfor each of the flexible tubes of Examples 2a–2e and ComparativeExamples 2a–2c. Through the observation, formation of projections 4 asshown in FIG. 2 was observed in each of the flexible tubes of Examples2a–2e and Comparative Examples 2a and 2b, but no formation ofprojections 4 was observed in the flexible tube of Comparative Example2c.

3. Measurement of Rate of Change in Bending Stiffness

The rate of change in the bending stiffness in the longitudinaldirection was measured for each of the flexible tubes of Examples 2a–2e.

For each flexible tube, first the flexible tube was divided into eightsections (i.e., first–eighth sections as shown in FIG. 13) which have anequal length (200 mm) in the longitudinal direction, and then thebending stiffness in “each” of the eight sections of the flexible tubewas measured according to the following method.

In the measurement, as shown in FIG. 15, first the flexible tube waslaid on two supporting-points located a distance L (200 mm) a part sothat both ends of one of the sections were supported by the twosupporting-points. Then, the magnitude of the pressing force F when thecentral point of the section was displaced downward by a predetermineddistance y (50 mm) was measured and defined as the bending stiffness ofeach section. Based on the measured value, the rate of change in thebending stiffness in the longitudinal direction of the flexible tube wascalculated. The results of the measurement are shown in the attachedTable 3.

4. Evaluation of Flexible Tube

(4-1) Insertion (Operationability) Test

An insertion test was carried out for each of the flexible tubes ofExamples 2a–2e and Comparative Examples 2a–2c to evaluateoperationability (i.e., degree of easiness in insertion operation) of anendoscope with the flexible tube.

Before carrying out the insertion test, endoscopes as shown in FIG. 1were prepared using the flexible tubes of Examples 2a–2e and ComparativeExamples 2a–2c. Further, a living body model having an internalstructure similar to an internal portion of a human body was prepared.Then, each of the prepared endoscopes was inserted into the internalportion of the living body model until its tip end (i.e., tip of anbendable tube 5) reaches a portion corresponding to a large intestine ofa human body. In the insertion test, the operationability of theendoscope during the insertion operation was evaluated in accordancewith the four rankings A–D given below.

-   Rank A:    -   It is possible to perform insertion operation very smoothly. (A        flexible tube of an endoscope of Rank A is considered to be best        suited for use as a flexible tube for an endoscope.)-   Rank B:    -   It is possible to perform insertion operation smoothly. (A        flexible tube of an endoscope of Rank B is considered to be        suited for use as a flexible tube for an endoscope.)-   Rank C:    -   It takes a relatively long time to complete insertion operation.        (A flexible tube of an endoscope of Rank C is considered to have        problems for use as a flexible tube for an endoscope.)-   Rank D:    -   It is difficult to complete insertion operation. (A flexible        tube of an endoscope of Rank D is considered to be unsuited for        use as a flexible tube for an endoscope.)

The results of the insertion test are shown in the attached Table 4.

(4-2) Chemical Resistance Test

A chemical resistance test was carried out for each of the flexibletubes of Example 2a–2e and Comparative Example 2a–2c. In the chemicalresistance test, 100L of 10% aqueous solution of iodine held at 25° C.was prepared first, and then each of the prepared flexible tubes wasimmersed in the aqueous solution for 200 hours. Then, the condition ofeach flexible tube was evaluated in accordance with the four rankingsA–D given below.

-   Rank A:    -   No Change in the Appearance; and    -   No Occurrence of Cracks and Blisters in Outer Cover.-   Rank B:    -   Slight Change in the Appearance; and    -   Occurrence of Blisters at a Few Spots of Outer Cover.-   Rank C:    -   Large Change in the Appearance; and    -   Occurrence of Blisters at Many Spots of Outer Cover.-   Rank D:    -   Extremely Large Change in the Appearance; and    -   Occurrence of a Large Number of Cracks and Blisters on Outer        Cover.

The evaluation result in this test is shown in the attached Table 4.

(4-3) Durability Test

A durability test was carried out to examine durability of each of theflexible tubes of Example 2a–2e and Comparative Example 2a–2c. In thedurability test, each of the flexible tubes was set to a state where theflexible tube was supported at its both ends, and in this state theoperation of bending by 90° was repeated 300 times for each flexibletube. Then, the degree of change in the flexibility after the repeatedoperation of bending was examined to evaluate the durability of theflexible tube in accordance with the four rankings A–D given below.

-   Rank A:    -   Almost No Change in Flexibility    -   (A flexible tube of Rank A is considered to have extremely high        durability.)-   Rank B:    -   Slight Lowering of Flexibility    -   (A flexible tube of Rank B is considered to have high        durability.)-   Rank C:    -   Large Lowering of Flexibility    -   (A flexible tube of Rank C is considered to have problems in the        durability.)-   Rank D:    -   Extremely Large Lowering of Flexibility; and    -   Occurrence of cracks and the like at many spots of the outer        cover.    -   (A flexible tube of Rank D is considered to be unsuited for use        as a flexible tube for an endoscope.)

The result of the durability test is shown in the attached Table 4.

(4-4) Evaluation

The results in the attached Tables 3 and 4 show that the flexible tubeaccording to the present invention (i.e., Examples 2a–2e) has excellentoperationability and high chemical resistance as well as highdurability. Further, the results in the attached Table 4 also show thatconventional flexible tubes (i.e., Comparative Examples 2a–2c) have somedrawbacks.

Specifically, the flexible tube of Comparative Example 2a has poorresistance to chemical. This drawback is considered to result from thefact that the outer layer 32 of the outer cover 3 was formed of thematerial having poor chemical resistance. Further, the flexible tube ofComparative Example 2b has poor operationability. Furthermore, theflexible tube of Comparative Example 2c has poor durability as well aspoor operationability. The poor durability of this flexible tube isconsidered to result from the fact that no projections 4 as shown inFIG. 2 were formed on the inner layer 31.

According to the present invention described above, appropriatematerials that are for each of layers of an outer cover 3 are used forpreparing the outer cover, and the outer cover 3 is provided onto thecore body so that each of the layers has appropriate thickness andshape. This structure and the selection of material make it possible toproduce a flexible tube for an endoscope that has high durability, highflexibility, and high chemical resistance as well as excellentoperationability.

Further, according to the present invention, the outer cover of theflexible tube is formed so that the thickness of at least one of layersconstituting the outer cover (laminate structure) varies in thelongitudinal direction, for example, gradually or stepwise. Thisconfiguration makes it possible for an operator to insert an insertionsection (flexible tube) of an endoscope into a body cavity of a livingbody with easy manipulation.

Furthermore, according to the present invention, a material having highelasticity is used for an intermediate layer of the outer cover. Thismakes it possible to give high flexibility to a flexible tube, thusenabling the operator to insert an insertion section of an endoscopemore easily.

Moreover, according to the present invention, a material having highresistance to chemical is used for an outer layer of the outer cover.This makes it possible to give high chemical resistance to a flexibletube.

In addition, according to the present invention, a material having highadhesion with a core body 2 is used for an inner layer of an outercover. This makes it possible to give high durability to a flexibletube.

IX. Seventh Embodiment (Flexible Tube 1G)

Next, a seventh embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 8. FIG. 8 is a sectional view whichshows a part of a flexible tube 1G according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.

An outer cover 3 of the flexible tube 1G has a laminate structurecomposed of inner, outer and intermediate layers 31–33. The inner andouter layers 31 and 32 have the same structures as those of the flexibletube 1A in the first embodiment, and this embodiment is different fromthe first embodiment in the structure of the intermediate layer 33. Thestructure of the intermediate layer 33 is described below in detail.

The intermediate layer 33 is formed between the inner layer 31 and theouter layer 32. As shown in FIG. 8, this intermediate layer 33 has afirst portion (first region) 31 a formed at a position closer to the tipend 12, and a second portion (second region) 33 b formed at a positioncloser to the base end 11. The first and second portions 33 a and 33 bare contiguous to each other through a boundary 34. Specifically, thefirst portion 33 a is formed within a region from the tip end 12 to theboundary 34, and the second portion 33 b is formed within a region fromthe boundary section 34 to the base end 11.

The first portion 33 a is different from the second portion 33 b and 33b in its physical property or chemical property. (Hereinafter, thephysical property and chemical property will be referred to simply as“property.”) However, the property within each of the first and secondportions 33 a and 33 b is substantially homogeneous. As a result of thisstructure, the property of the intermediate layer 33 variessubstantially stepwise at the boundary 34. Such a difference in theproperty between the first and second portions 33 a and 33 b can beobtained by constituting the first and second portions 33 a and 33 bwith different materials.

The lengths of the first and second portions 33 a and 33 b in thelongitudinal direction may differ depending on the type of an endoscopeor the like. However, in this invention, it is preferable that thelength of the first portion 33 a is in the range of about 50 to 1000 mm,and more preferably about 100 to 700 mm. Further, it is preferable thatthe length of the second portion 33 b is in the range of about 50 to1000 mm, and more preferably 100 to 700 mm.

In addition, in this invention, it is preferable that the first portion33 a is formed of a material having a lower hardness (stiffness) thanthat of the second portion 33 b. With this arrangement, the tip sideportion of the outer cover 3 where the first portion 33 a is formed hasa lower stiffness against tension, bending and the like than that of thebase side portion of the outer cover 3 where the second portion 33 b isformed. Therefore, by forming the outer cover 3 so as to have twodistinct portions (i.e., first and second portion 33 a and 33 b), itbecomes possible to give the tip side region of a flexible tube a higherflexibility than that of the base side region.

According to the flexible tube 1G having the intermediate layer 33 asdescribed, the flexible tube 1G has a high “stiffness” in the portionnear the base end 11 (where the second portion 33 b is formed) so that apush-in force and the rotational force applied by the operator aresufficiently transmitted to the tip end 12, while it has a high“flexibility” in the portion near the tip end 12 (where the firstportion 33 a is formed) so that the tip side region of the flexible tubeis smoothly inserted into and follows the body cavity having curvedform. This structure makes it possible to improve the operationabilityof the endoscope when inserting the insertion section (flexible tube)into an internal portion of the living body. Accordingly, when anendoscope with the flexible tube having the structure as described aboveis used during an endoscopic examination, it is possible to reduceburden on a patient, since the operator can safely and smoothly performthe insertion operation.

In this invention, it is preferable the intermediate layer 33 has ahigher elasticity than that of the outer layer 32, and more preferablythe intermediate layer 33 has a higher elasticity than that of any oneof the inner and outer layers 31 and 32. With this arrangement, theintermediate layer 33 functions as a cushioning layer (cushioning means)between the inner layer 31 and the outer layer 32. (In the following,such a function given by the intermediate layer 33 is referred to as“cushioning function.”) Accordingly, by forming the, intermediate layer33 as described above, it is possible to give higher flexibility to theflexible tube.

Hereinafter, the cushioning function of the intermediate layer 33 isdescribed in more detail. When the flexible tube 1G is bent by anexternal force, the high elastic force is generated in the bentintermediate layer 33 through the deformation thereof The generatedelastic force is transmitted effectively to the inner layer 31 and theouter layer 32, respectively, since the intermediate layer 33 issandwiched between the inner layer 31 and the outer layer 32 each ofwhich has relatively low elasticity. When the external force has beenremoved, the bent flexible tube 1G is restored to its original shape bythe high elastic force generated in the bent intermediate layer 33. Inthis connection, it is to be noted that the restoration of the flexibletube into its original shape is achieved by the cushioning function ofthe intermediate layer 33, and that such a cushioning function gives theflexible tube high flexibility.

In this embodiment, a constituent material for the intermediate layer 33is not particularly limited. Examples of such material include variousresins having elasticity such as polyvinyl chloride, polyolefine (e.g.,polyethylene, polypropylene, ethylene-vinylacetate copolymer and thelike), polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate and the like), polyurethane, polystyreneresin, fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer and the like), polyimide, and thelike; and various elastomers such as polyurethane-based elastomer,polyester-based elastomer, polyolefine-based elastomer, polyamide-basedelastomer, polystyrene-based elastomer, fluorine-based elastomer,silicone rubber, fluororubber, latex rubber, and the like. These can beused alone or as a mixture of two or more thereof. In this invention, amaterial containing at least one of low hardness polyurethane-basedelastomer, low hardness polyolefin-based elastomer, and low hardnesspolyester-based elastomer is preferably used to form the intermediatelayer 33, since such elastomers have high elasticity.

Although the intermediate layer 33 in this embodiment is given a singlelayer construction, it may be given a construction of two or morelayers.

In this invention, the average thickness of the intermediate layer 33 isnot particularly limited, but the average thickness is preferably in therange of 0.05 to 0.8 mm, and more preferably in the range of 0.05 to 0.4mm.

X. Eighth Embodiment (Flexible Tube 1H)

Next, an eighth embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 9. FIG. 9 is a sectional view whichshows a part of a flexible tube 1H according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.

As shown in FIG. 9, the outer cover 3 of the flexible tube 1H has alaminate structure composed of inner, outer and intermediate layers31–33. Each of the inner and outer layers 31 and 32 has a substantiallyuniform thickness over its entire region, and has almost homogeneousproperty over its entire region. The intermediate layer 33 has a firstportion (first region) 33 a formed in a tip side region, and a secondportion (second region) 33 b formed in a base side region. The first andsecond portions 33 a and 33 b of the intermediate layer 33 havedifferent properties. As shown in FIG. 9, the first and second portions33 a and 33 b are contiguous to each other through a boundary part(property-varying region) 37 formed between the first and secondportions 33 a and 33 b, and they are arranged along the longitudinaldirection. In this invention, it is preferable that the first portion 33a is formed of a material having a lower hardness (stiffness) than thatof a material constituting the second portion 33 b.

Within the boundary part 37, its property gradually varies in thelongitudinal direction. A tip end portion of the boundary part 37 hassubstantially the same property as that of the first portion 33 a, whilea base end portion of the boundary part 37 has substantially the sameproperty as that of the second portion 33 b.

The boundary part 37 described above is formed through an extrusionmolding process. Specifically, a mixture of a constituent material forthe first portion 33 a and a constituent material for the second portion33 b is prepared first, and then the mixture is fed during the extrusionmolding while gradually changing the mixing rate of these materials. Inthis way, the outer cover 3 which has a layer with a boundary part whereits property changes gradually in the longitudinal direction is formed.However, the structure of the boundary part 37 is not limited to that asdescribed above. For example, the boundary part 37 may be formed as alaminated part (composite part) composed of two halves. In this case, afirst half is formed of a material having the same property as the firstportion 33 a such that its thickness gradually decreases in thedirection from the tip side to the base side. Further, a second half isformed of a material having the same property as the second portion 33 bsuch that its thickness gradually decreases in the direction from thebase side to the tip side.

The length in the longitudinal direction of the boundary part 37 is notparticularly limited. For example, when the boundary part 37 is formedso as to have a relatively large length, it is possible give a flexibletube a stiffness which varies more gradually in the longitudinaldirection. However, in this invention, the length of the boundary part37 is preferably in the range of 5 to 600 mm, and more preferable in therange of 10 to 400 mm.

By configuring a flexible tube as described above, it is possible toform an intermediate layer so as to have relatively low stiffness in thefirst portion 33 a located at the tip side, and have relatively highstiffness in the second portion 33 b located at the base side. Inaddition, it is also possible to form the intermediate layer 33 suchthat a boundary part (property-varying region) 37 where its propertyvaries gradually along the longitudinal direction is formed between thefirst and second portions 33 a and 33 b.

According to the flexible tube as described above, due to the formationof the boundary part 37 as well as the homogeneous formation of theinner and outer layers 31 and 32, the stiffness of the flexible tube 1Hgradually varies within the boundary part 37 and in the vicinity of itsboth ends. This structure makes it possible to provide a flexible tubewhose stiffness (e.g., bending stiffness) varies more gradually alongthe longitudinal direction as compared with the flexible tube 1G (FIG.8) of the seventh embodiment described above. When an endoscope with theflexible tube having the structure as described above is used during anendoscopic examination, it is possible to reduce burden on a patient,since the operator can more safely and smoothly insert the insertionportion of the endoscope into a body cavity of the patient.

Further, according to the flexible tube 1H of this embodiment, there isno spot where the stiffness varies abruptly, since the intermediatelayer 33 has the boundary part (property-varying region) 37, and theinner and outer layers 31 and 32 are formed almost homogeneously.Therefore, a push-in force or a rotational force applied by the operatorfrom the base side will not be concentrated at any portion, so that theforce can be transmitted sufficiently to the tip end of an endoscopewith the flexible tube. In addition, because of the absence of a spotwhere the stiffness varies abruptly, tendency of the flexible tube tocurl or twist will not concentrate at any portion of the flexible tube.

In addition, according to the flexible tube of this embodiment, each ofthe inner and outer layers 31 and 32 is formed homogeneously over itsentire region. This formation makes it possible for the inner layer 31to have a uniform and high adhesion with the core body 2 over its entireregion, and also makes it possible for the outer layer 32 to haveuniform and high resistance to chemical over its entire length.

XI. Ninth Embodiment (Flexible Tube 1I)

Next, a ninth embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 10. FIG. 10 is a sectional view whichshows a part of a flexible tube 1I according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.

As shown in FIG. 10, an outer cover 3 of the flexible tube 1I has alaminate structure composed of inner, outer and intermediate layers31–33. Each of the inner and outer layers 31 and 32 has a substantiallyuniform thickness and a substantially homogeneous property over itsentire region. The intermediate layer 33 has three distinct portions(i.e., first–third portions 33 a–33 c). The first portion (first region)33 a is formed at the tip side, the third portion (third region) 33 c isformed at the base side, and the second portion (second region) 33 b isformed between the first portion 33 a and the third portion 33 c. Eachof the first and third portions 33 a and 33 c is different from thesecond portion 33 b in its property. In this invention, it is preferablethat the first portion 33 a is formed of a material having a lowerhardness (stiffness) than that of a material constituting the secondportion 33 b. Further, it is also preferable that the second portion 33b is formed of a material having a lower hardness (stiffness) than thatof a material constituting the third portion 33 c.

In addition, the intermediate layer 33 has two boundary parts(property-varying regions) 37 which are formed between the first andsecond portions 33 a and 33 b and between the second and third portions33 b and 33 c, respectively. Each of the boundary parts 37 hassubstantially the same structure as that of the intermediate layer 33 ofthe flexible tube 1H (FIG. 9) in the eighth embodiment described above,and formed in the same manner as in the eighth embodiment.

In this embodiment, the length of each of the portions of theintermediate layer 33 is not particularly limited. However, it ispreferable that the length of the first portion 33 a is preferably inthe range of about 50 to 1000 mm, and more preferably in the range ofabout 100 to 700 mm. Further, it is preferable that the length of thesecond portion 33 b is preferably in the range of about 50 to 800 mm,and more preferably in the range of about 100 to 600 mm. Furthermore, itis preferable that the length of the third portion 33 c is preferably inthe range of about 50 to 1000 mm, and more preferably in the range ofabout 200 to 1000 mm.

According to the flexible tube 1I having the structure described above,the intermediate layer 33 has a relatively low stiffness in the firstportion 33 a located at the tip side, has a relatively high stiffness inthe third portion 33 c located at the base side, and has a mediumstiffness in the second portion 33 b between the first and secondportions 33 a and 33 b. In addition, the stiffness of the intermediatelayer 33 gradually varies within each of the boundary parts 37 formedbetween the first and second portions 33 a and 33 b and between thesecond and third portions 33 b and 33 c, respectively.

Further, according to the flexible tube 1I described above, as a resultof the formation of the three distinct portions 33 a–33 c, the stiffnessof the flexible tube 1I varies along the longitudinal direction inroughly three stages. In addition, as a result of the formation of thetwo boundary parts (property-varying regions) 37, the stiffness of theflexible tube 1I varies more gradually along the longitudinal direction.Accordingly, the stiffness of the flexible tube 1I in this embodimentvaries along the longitudinal direction in a more gradual manner ascompared with the flexible tube 1H (FIG. 9) of the eighth embodiment inwhich the stiffness varies in roughly “two” stages. Therefore, when anendoscope with the flexible tube 1I having the structure as describedabove is used during an endoscopic examination, it is possible toreliably reduce burden on a patient, since the operator can more safelyand smoothly insert an insertion portion of an endoscope.

XII. Tenth Embodiment (Flexible Tube 1J)

Next, a tenth embodiment of the flexible tube for an endoscope will bedescribed with reference to FIG. 11. FIG. 11 is a sectional view whichshows a part of a flexible tube 1J according to the present invention,in which illustration of projections 4 as shown in FIG. 2 is omitted,and structure of a reticular tube 22 is simply illustrated as a layer.In this figure, the right-hand side corresponds to the side of the baseend 11 shown in FIG. 1 (i.e., side closer to an operator), and theleft-hand side corresponds to the side of tip end 12 shown in FIG. 1.

As shown in FIG. 11, an outer cover 3 of the flexible tube 1J has alaminate structure composed of inner, outer and intermediate layers31–33. Each of the inner and intermediate layers 31 and 33 hashomogeneous formation and a substantially uniform thickness over itsentire region. The outer layer 32 has three distinct portions (i.e.,first–third portions 32 a–32 c). The first portion (first region) 32 ais formed at the tip side, the third portion (third region) 32 c isformed at the base side, and the second portion (second region) 32 b isformed between the first portion 32 a and the third portion 32 c. Eachof the first and third portions 32 a and 32 c is different from thesecond portion 32 b in its property. In this invention, it is preferablethat the first portion 32 a is formed of a material having a lowerhardness (stiffness) than that of a material constituting the secondportion 32 b. Further, it is also preferable that the second portion 32b is formed of a material having a lower hardness (stiffness) than thatof a material constituting the third portion 32 c. In addition, in thisinvention, it is preferable that each of the first–third portions 32a–32 c of the outer layer 32 has high resistance to chemical.

The outer layer 32 has two boundary parts (property-varying regions) 36which are formed between the first and second portions 32 a and 32 b andbetween the second and third portions 32 b and 32 c, respectively. Eachof the boundary parts 36 has substantially the same structure as that ofthe intermediate layer 33 of the flexible tube 1H (FIG. 9) in the eighthembodiment described above, and formed in the same manner as in theeighth embodiment.

In this embodiment, the length of each of the portions of the outerlayer 32 is not particularly limited. However, it is preferable that thelength of the first portion 32 a is preferably in the range of about 50to 1000 mm, and more preferably in the range of about 100 to 700 mm.Further, it is preferable that the length of the second portion 32 b ispreferably in the range of about 50 to 800 mm, and more preferably inthe range of about 100 to 600 mm. Furthermore, it is preferable that thelength of the third portion 32 c is preferably in the range of about 50to 1000 mm, and more preferably in the range of about 200 to 1000 mm.

In the flexible tube 1J having the structure described above, the outerlayer 32 has a relatively low stiffness in the first portion 32 alocated at the tip side, has a relatively high stiffness in the thirdportion 32 c located at the base side, and has a medium stiffness in thesecond portion 32 b between the first and third portions 32 a and 32 c.In addition, the stiffness of the outer layer 32 gradually varies withineach of the boundary parts (property-varying regions) 36 formed betweenthe first and second portions 32 a and 32 b and between the second andthird portions 32 b and 32 c, respectively. Therefore, according to theflexible tube 1J described above, it is possible to achieve the sameadvantages as those described with respect to the flexible tube 1I (FIG.10) in the ninth embodiment.

In addition, according to the flexible tube 1J of this embodiment, eachof the inner and intermediate layers 31 and 33 is formed homogeneouslyover its entire region. This formation makes it possible for the innerlayer 31 to have a uniform and high adhesion with the core body 2 overits entire region, and also makes it possible for the intermediate layer33 to have uniform and high flexibility over its entire length.

XIII. Eleventh Embodiment (Flexible Tube 1K)

Next, an eleventh embodiment of the flexible tube for an endoscope willbe described with reference to FIG. 12. FIG. 12 is a sectional viewwhich shows a part of a flexible tube 1K according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

As shown in FIG. 12, an outer cover 3 of the flexible tube 1K has alaminate structure composed of inner, outer and intermediate layers31–33.

The intermediate layer 33 has a substantially uniform thickness over itsentire region, and is formed homogeneously over its entire region.

The outer layer 32 has the same structure as that described withreference to the tenth embodiment shown in FIG. 11. Specifically, theouter layer 32 has three distinct portions (i.e., first–third portions32 a–32 c). The first portion (first region) 32 a is formed at the tipside, the third portion (third region) 32 c is formed at the base side,and the second portion (second region) 32 b is formed between the firstportion 32 a and the third portion 32 c. Each of the first and thirdportions 32 a and 32 c is different from the second portion 32 b in itsproperty. In this invention, it is preferable that the first portion 32a is formed of a material having a lower hardness (stiffness) than thatof a material constituting the second portion 32 b. Further, it is alsopreferable that the second portion 32 b is formed of a material having alower hardness (stiffness) than that of a material constituting thethird portion 32 c. In addition, in this invention, it is preferablethat each of the first–third portions 32 a–32 c of the outer layer 32has high resistance to chemical.

Further, the outer layer 32 has two boundary parts (property-varyingregions) 36 which are formed between the first and second portions 32 aand 32 b and between the second and third portions 32 b and 32 c,respectively. Each of the boundary parts 36 has substantially the samestructure as that of the intermediate layer 33 of the flexible tube 1H(FIG. 9) in the eighth embodiment described above, and formed in thesame manner ass in the eighth embodiment.

The inner layer 31 has two distinct portions (i.e., first and secondportions 31 a and 31 b). The first portion (first region) 31 a is formedat the tip side, and the second portion (second region) 31 b is formedat the base side. The first portion 31 a is different from the secondportion 31 b in its property. In this invention, it is preferable thatthe first portion 31 a is formed of a material having a lower hardness(stiffness) than that of a material constituting the second portion 31b. Further, it is also preferable that each of the first and secondportions 31 a and 31 b of the inner layer 31 is formed of a materialhaving high adhesion with a core body 2, that is, a material which areeasily formed into a layer with projections 4 as shown in FIG. 2 throughextrusion molding.

In addition, the inner layer 31 has a boundary part (property-varyingregion) 35 which is formed between the first and second portions 31 aand 31 b. The boundary part 35 has substantially the same structure asthat of the intermediate layer 33 of the flexible tube 1H (FIG. 9) inthe eighth embodiment described above, and formed in the same manner asin the eighth embodiment.

In this embodiment, the length of the first and second portions 31 a and31 b of the inner layer 31 is not particularly limited. However, it ispreferable that the length of the first portion 31 a is preferably inthe range of about 50 to 1000 mm, and more preferably in the range ofabout 500 to 1000 mm. Further, it is preferable that the length of thesecond portion 31 b is preferably in the range of about 50 to 1000 mm,and more preferably in the range of about 400 to 1000 mm.

According to the flexible tube 1K having the structure described above,the outer cover 3 of the flexible tube 1K has different stiffness in thefollowing four regions (1)–(4). (The stiffness of the flexible tube 1Kincreases in this order in the longitudinal direction.)

-   (1) A region of the outer cover 3 where both the first portion 32 a    of the outer layer 32 and the first portion 31 a of the inner layer    31 are formed, and where these portions partly face each other.-   (2) A region of the outer cover 3 where both the second portion 32 b    of the outer layer 32 and the first portion 31 a of the inner layer    31 are formed, and where these portions partly face each other.-   (3) A region of the outer cover 3 where both the second portion 32 b    of the outer layer 32 and the second portion 31 b of the inner layer    31 are formed, and where these portions partly face each other.-   (4) A region of the outer cover 3 where both the third portion 32 c    of the outer layer 32 and the second portion 31 b of the inner layer    31 are formed, and where these portions partly face each other.

Therefore, the flexibility of the flexible tube 1K varies along thelongitudinal-direction in roughly four stages. Further, as a result ofthe formation of the boundary parts (property-varying regions) 35 and36, the stiffness of the flexible tube varies more gradually along thelongitudinal direction. Accordingly, the stiffness of the flexible tube1K in this embodiment varies along the longitudinal direction in a moregradual manner as compared with the flexible tube 1I (FIG. 10) of theninth embodiment in which the stiffness varies in roughly “three”stages. Therefore, when an endoscope with the flexible tube having thestructure as described above is used during an endoscopic examination,it is possible to reliably reduce burden on a patient, since theoperator can more safely and smoothly insert the insertion portion ofthe endoscope into a body cavity of the patient.

Further, according to the flexible tube 1K having the structuredescribed above, the outer cover 3 of the flexible tube 1K is formedsuch that the boundary part 35 of the inner layer 31 is not locatedbelow the boundary parts 36 of the outer layer 32 in the thicknessdirection. In other words, the outer cover 3 of the flexible tube isformed such that the boundary part 35 of the inner layer 31 and theboundary part 36 of the outer layer 32 are alternately located in thelongitudinal direction of the outer cover 3. This arrangement makes itpossible for a flexible tube to have a stiffness that varies moregradually in the longitudinal direction.

XIV. Examples of Modification

In the above, the flexible tube for an endoscope according to thepresent invention was described in detail. However, it is to be notedthat this invention is not limited to the embodiments described above.

For example, one or more of layers of the outer cover 3 may be formedusing materials which contain the same principal material (main polymer)but which are different in molecular weight, the content of additives(e.g., plasticizer), or the like. Alternatively, one or more of layersof the outer cover 3 may also be formed of materials which contain thesame components but which are different in density. In this way, it isalso possible to form an outer cover 3 such that a layer of the outercover 3 has distinct portions having different properties.

Further, the structure of each layer of the outer cover 3 is notparticularly limited. For example, an outer cover 32 of a flexible tubemay be formed such that any one of layers has regions having differentproperties. Further, an outer cover of a flexible tube may also beformed such that each of two or more of layers has regions havingdifferent properties.

Furthermore, the structure of an outer cover 3 described above is notparticularly limited. For example, an outer cover of a flexible tube maybe formed such that a part of the outer cover has a laminate structurecomposed of a plurality of layers.

In addition, for example, the flexible tube for an endoscope accordingto the present invention may be applied to other site of the endoscopesuch as a flexible tube for a light guide connected to a light sourcedevice.

XV. Examples of Seventh–Eleventh Embodiments

Next, specific examples of the seventh–eleventh embodiments of thepresent invention will be described below.

1. Preparation of Flexible Tube for an Endoscope

Example 3a

First, a coil 21 having an outer diameter of 9.9 mm and an innerdiameter of 9.6 mm was prepared by winding a band-shaped stainless steelmaterial having a width of 3 mm. Next, stainless steel fine wires 23 atleast one of which had been given a coating of a polyamide resin andeach of which had a diameter of 0.1 mm were prepared, and then usingthese fine wires a plurality of bundles of ten fine wires were prepared.These bundles of the ten fine wires 23 were woven together in a latticemanner to obtain a reticular tube 22. Then, the obtained reticular tube22 was provided on the prepared coil 21 so that the outer periphery ofthe coil 21 was covered with the reticular tube 22. In this way, a corebody 2 was prepared.

Next, using an extrusion-molding machine, an outer cover 3 composed ofinner, outer and intermediate layers 31–33 was provided on the outerperiphery of the core body 2 so that the core body 2 was covered withthe outer cover 3. In this way, a flexible tube for an endoscope with alength of 1.6 m was prepared. In this connection, it is to be noted thatthe length of 1.6 m means the length of an available (effective) portionof the flexible tube that can be used for a flexible tube for anendoscope, that is the length of 1.6 m means an available (effective)length of the flexible tube. Therefore, the actually prepared flexibletube had a length more than 1.6 m by including additional portions atthe both ends of the available portion of the flexible tube (See FIG.14). In this regard, however, it goes without saying that the availablelength is not limited to 1.6 m mentioned above.

The details of each of the inner, outer and intermediate layers are asfollows.

<Inner Layer>

The inner layer 31 was formed so as to have a single region with auniform thickness. The thickness and a constituent material of the innerlayer 31 were as follows.

-   Thickness: 0.2 mm-   Material: A medium hardness polyurethane-based elastomer having a    hardness of A81. (Hardness was measured in accordance with JIS K    7311.)

<Outer Layer>

The outer layer 32 was formed so as to have a single region with auniform thickness. The thickness and a constituent material of the outerlayer 32 were as follows.

-   Thickness: 0.1 mm-   Material: A High hardness polyester-based elastomer having a    hardness of A92 (Hardness was measured in accordance with JIS K    7311.)

<Intermediate Layer>

The intermediate layer 33 was formed so as to have a uniform thickness(0.3 mm) and to have first, second and third portions 33 a–33 c. Thefirst portion 33 a was formed at the tip side, the second portion 33 bwas formed between the first and third portions 33 a and 33 c, and thethird portion 33 c was formed at the base side. The first portion 33 awas contiguous to the second portion 33 b through a boundary 34, and thethird portion 33 c was contiguous to the second portion 33 b through aboundary 34. The details of each of the portions 33 a–33 c are asfollows.

--First Portion--

Length: 440 mm

Material: A low hardness polyurethane-based elastomer having a hardnessof A68. (Hardness was measured in accordance with JIS K 7311.)

--Second Portion--

Length: 530 mm

Material: A medium hardness polyurethane-based elastomer having ahardness of A82. (Hardness was measured in accordance with JIS K 7311.)

--Third Portion--

Length: 630 mm

Material: A high hardness polyurethane-based elastomer having a hardnessof A90. (Hardness was measured in accordance with JIS K 7311.)

Example 3b

A flexible tube for an endoscope was prepared in the same manner as inExample 3a except that the configuration of an intermediate layer 33 waschanged as follows.

--First Portion--

Length: 450 mm

Material: A low hardness polyurethane-based elastomer having a hardnessof A68. (Hardness was measured in accordance with JIS K 7311.)

--Second Portion--

Length: 300 mm

Material: A medium hardness polyurethane-based elastomer having ahardness of A82. (Hardness was measured in accordance with JIS K 7311.)

--Third Portion--

Length: 450 mm

Material: A high hardness polyurethane-based elastomer having a hardnessof A90. (Hardness was measured in accordance with JIS K 7311.)

--Boundary Parts--

In this Example, two boundary parts 37 each of which had a length of 200mm were formed in the intermediate layer 33. One of the boundary part 37was formed between the first and second portions 33 a and 33 b, and theother boundary part 37 was formed between the second and third portions33 b and 33 c. Each of the boundary parts 37, was formed through anextrusion molding process so that its property gradually changes in thelongitudinal direction. Specifically, first, a mixture of a constituentmaterial for the first portion 33 a and a constituent material for thesecond portion 33 b was fed in an extrusion molding machine whilegradually changing the mixing rate of these materials. Further, amixture of a constituent material for the second portion 33 b and aconstituent material for the third portion 33 c was fed in the extrusionmolding machine while gradually changing the mixing rate of thesematerials.

Example 3c

A flexible tube for an endoscope was prepared in the same manner as inExample 3a except that the configuration of each of outer andintermediate layer 32 and 33 was changed as follows.

<Outer Layer>

In this Example, the outer layer 32 was formed so as to have a uniformthickness (0.1 mm), and so as to have three portions (i.e., first,second and third portions 32 a–32 c) and two boundary parts(property-varying regions) 36. The details of each of the portions 32a–32 c and the boundary parts 36 are as follows.

--First Portion--

Length: 450 mm

Material: A low hardness polyolefine-based elastomer having a hardnessof A76. (Hardness was measured in accordance with JIS-K 7311.)

--Second Portion--

Length: 300 mm

Material: A medium hardness polyolefine-based elastomer having ahardness of A85. (Hardness was measured in accordance with JIS K 7311.)

--Third Portion--

Length: 450 mm

Material: A high hardness polyolefine-based elastomer having a hardnessof A95. (Hardness was measured in accordance with JIS K 7311.)

--Boundary Part-

In this Example, each of the boundary parts 36 had a length of 200 mm.One of the boundary part 36 was formed between the first and secondportions 32 a and 32 b, and the other boundary part 36 was formedbetween the second and third portions 32 b and 32 c.

<Intermediate Layer>

In this Example, the intermediate layer 33 was formed so as to have asingle region with a uniform thickness (0.3 mm). A constituent materialof the intermediate layer 33 was as follows.

Material: A low hardness polyurethane-based elastomer having a hardnessof A78. (Hardness was measured in accordance with JIS K 7311.)

Example 3d

A flexible tube for an endoscope was prepared in the same manner as inExample 3c except that the configuration of an inner layer 31 of anouter cover 3 was changed as follows.

In this Example, the inner layer 31 was formed so as to have a uniformthickness (0.2 mm), and so as to have two portions (i.e., first andsecond portions 31 a and 31 b) and a boundary part (property-varyingregion) 35. The details of each of the portions 31 a and 31 b and theboundary part 35 are as follows.

--First Portion--

Length: 600 mm

Material: A medium hardness polyurethane-based elastomer having ahardness of A82. (Hardness was measured in accordance with JIS K 7311.)

--Second Portion--

Length: 600 mm

Material: A high hardness polyurethane-based elastomer having a hardnessof A91. (Hardness was measured in accordance with JIS K 7311.)

--Boundary Parts--

In this Example, the boundary part 35 having a length of 400 mm wasformed between the first and second portions 31 a and 31 b.

Comparative Example 3a

A core body 2 was prepared in the same manner as in Example 3a. Then,using an extrusion-molding machine, an outer cover 3 composed of innerand outer layers 31 and 32 was provided on the outer periphery of thecore body 2 so that the core body 2 was covered with the outer cover 3.In this way, a flexible tube for an endoscope with a length of 1.6 m wasprepared. The details of each of the layers 31 and 32 of the outer cover3 are as follows.

<Inner Layer>

The inner layer 31 was formed so as to have a single region with auniform thickness. The thickness and a constituent material of the innerlayer 31 were as follows.

-   Thickness: 0.3 mm-   Material: A medium hardness polyurethane-based elastomer having a    hardness of A81. (Hardness was measured in accordance with JIS K    7311.)

<Outer Layer>

The outer layer 32 was formed so as to have a single region with auniform thickness. The thickness and a constituent material of the outerlayer 32 were as follows.

-   Thickness: 0.3 mm-   Material: A low hardness polyurethane-based elastomer having a    hardness of A68. (Hardness was measured in accordance with JIS K    7311.)

Comparative Example 3b

A flexible tube for an endoscope was prepared in the same manner as inComparative Example 3a except that a constituent material for each ofinner and outer layers 31 and 32 was changed as follows.

<Inner Layer>

-   Material: A medium hardness polyurethane-based elastomer having a    hardness of A81. (Hardness was measured in accordance with JIS K    7311.)

<Outer Layer>

-   Material: A high hardness polyester-based elastomer having a    hardness of A92. (Hardness was measured in accordance with JIS K    7311.)

Comparative Example 3c

A flexible tube for an endoscope was prepared in the same manner as inComparative Example 3a except that a constituent material for each ofinner and outer layers 31 and 32 was changed as follows.

<Inner Layer>

-   Material: A high hardness polyurethane-based elastomer having a    hardness of A90. (Hardness was measured in accordance with JIS K    7311.)

<Outer Layer>

-   Material: A high hardness polyester-based elastomer having a    hardness of A92. (Hardness was measured in accordance with JIS K    7311.)    2. Observation of the Prepared Flexible Tubes

An observation of the cross-section of the outer cover was carried outfor each of the flexible tubes of Examples 3a–3d and ComparativeExamples 3a–3c. Through the observation, formation of projections 4 asshown in FIG. 2 was observed in each of the flexible tubes of Examples3a–3d and Comparative Examples 3a and 3b, but no formation ofprojections 4 was observed in the flexible tube of Comparative Example3c.

3. Measurement of Rate of Change in Bending Stiffness

The rate of change in the bending stiffness in the longitudinaldirection was measured for each of the flexible tubes of Examples 3a–3d.

For each flexible tube, first the flexible tube was divided into ninesections (i.e., first–ninth sections as shown in FIG. 14) which have anequal length (177 mm) in the longitudinal direction, and then thebending stiffness in “each” of the nine sections of the flexible tubewas measured according to the following method.

In the measurement, as shown in FIG. 15, first the flexible tube waslaid on two supporting-points located a distance L (177 mm) a part sothat both ends of one of the sections were supported by the twosupporting-points. Then, the magnitude of the pressing force F when thecentral point of the section was displaced downward by a predetermineddistance y (50 mm) was measured and defined as the bending stiffness ofthe section. Based on the measured value, the rate of change in thebending stiffness in the longitudinal direction of the flexible tube wascalculated. The results of this measurement are shown in the attachedTable 5.

4. Evaluation of Flexible Tube

(4-1) Insertion (Operationability) Test

An insertion test was carried out for each of the flexible tubes ofExamples 3a–3d and Comparative Examples 3a–3c to evaluateoperationability of an endoscope with the flexible tube during insertionof the endoscope.

Before carrying out the insertion test, endoscopes as shown in FIG. 1were prepared using the flexible tubes of Examples 3a–3d and ComparativeExamples 3a–3c. Further, a living body model having an internalstructure similar to an internal portion of a human body was prepared.Then, each of the prepared endoscopes was inserted into the internalportion of the living body model until its tip end (i.e., tip of anbendable tube 5) reaches a portion corresponding to a large intestine ofa human body. In the insertion test, the operationability duringinsertion of the endoscope was evaluated in accordance with the fourrankings A–D given below.

-   Rank A:    -   It is possible to perform insertion operation very smoothly. (A        flexible tube of an endoscope of Rank A is considered to be best        suited for use as a flexible tube for an endoscope.)-   Rank B:    -   It is possible to perform insertion operation smoothly. (A        flexible tube of an endoscope of Rank B is considered to be        suited for use as a flexible tube for an endoscope.)-   Rank C:    -   It takes a relatively long time to complete insertion operation.        (A flexible tube of an endoscope of Rank C is considered to have        problems for use as a flexible tube for an endoscope.)-   Rank D:    -   It is difficult to complete insertion operation. (A flexible        tube of an endoscope of Rank D is considered to be unsuited for        use as a flexible tube for an endoscope.)

The results of the insertion test are shown in the attached Table 6.

(4-2) Chemical Resistance Test

A chemical resistance test was carried out for each of the flexibletubes of Example 3a–3d and Comparative Example 3a–3c. In this test, 100L of 10% aqueous solution of iodine held at 25° C. was prepared first,and then each of the prepared flexible tubes was immersed in the aqueoussolution for 200 hours. Then, the condition of each flexible tube wasevaluated in accordance with the four rankings A–D given below.

-   Rank A:    -   No Change in the Appearance; and    -   No Occurrence of Cracks and Blisters in Outer Cover.-   Rank B:    -   Slight Change in the Appearance; and    -   Occurrence of Blisters at a Few Spots of Outer Cover.-   Rank C:    -   Large Change in the Appearance; and    -   Occurrence of Blisters at Many Spots of Outer Cover.-   Rank D:    -   Extremely Large Change in the Appearance; and    -   Occurrence of a Large Number of Cracks and Blisters on Outer        Cover.

The evaluation result in this test is shown in the attached Table 6.

(4-3) Durability Test

A durability test was carried out for each of the flexible tubes ofExamples 3a–3d and Comparative Examples 3a–3c. In the durability test,each of the flexible tubes was set to a state where the flexible tubewas supported at its both ends, and in this state the operation ofbending by 90° was repeated 300 times. Then, the degree of change in theflexibility after the repeated operation of bending was examined toevaluate the durability of each flexible tube in accordance with thefour rankings A–D given below.

-   Rank A:    -   Almost No Change in Flexibility    -   (A flexible tube of Rank A is considered to have extremely high        durability.)-   Rank B:    -   Slight Lowering of Flexibility    -   (A flexible tube of Rank B is considered to have high        durability.)-   Rank C:    -   Large Lowering of Flexibility    -   (A flexible tube of Rank C is considered to have problems in its        durability.)-   Rank D:    -   Extremely Large Lowering of Flexibility; and    -   Occurrence of cracks and the like at many spots of the outer        cover.    -   (A flexible tube of Rank D is considered to be unsuited for use        as a flexible tube for an endoscope.)

The result of the durability test is shown in the attached Table 6.

(4-4) Evaluation

The results in the attached Tables 5 and 6 show that the flexible tubeaccording to the present invention (i.e., Examples 3a–3d) has excellentoperationability and high chemical resistance as well as highdurability. Further, the results in Table 6 also show that conventionalflexible tubes (i.e., Comparative Examples 3a–3c) have some drawbacks.

Specifically, the flexible tube of Comparative Example 3a has poorchemical resistance as well as poor operationability. The poor chemicalresistance of this flexible tube is considered to result from the factthat the outer layer of the outer cover is made of the material havingpoor resistance to chemical. Further, the flexible tube of ComparativeExample 3b has poor operationability. Furthermore, the flexible tube ofComparative Example 3c has poor durability as well as pooroperationability. The poor durability of this flexible tube isconsidered to result from the fact that projections 4 as shown in FIG. 2have not been formed on the inner layer 31.

According to the present invention described above, appropriatematerials that are suitable for each of layers of an outer cover areused for preparing the outer cover, and the outer cover is provided ontothe core body so that each of the layers has appropriate thickness andshape. This structure and the selection of material make it possible toproduce a flexible tube for an endoscope that has high durability, highflexibility and high chemical resistance as well as excellentoperationability.

Further, according to the present invention, at least one of layers ofan outer cover 3 has at least two distinct portions and a boundary partalong its longitudinal direction, and one of the portions is contiguousto the other portion through the boundary part. In this layer, one ofthe portions is different from the other portion adjacent thereto inphysical property or chemical property. This configuration makes itpossible for a flexible tube to have a stiffness (flexibility) whichgradually varies in its longitudinal direction.

According to an endoscope having the flexible tube as described above,since the flexible tube has a higher stiffness in a portion closer tothe base end, it is possible to fully transmit to the tip end of theendoscope the push-in force and the rotational force applied by anoperator. On the other hand, since the flexible tube has a higherflexibility in a portion closer to the tip end, it is also possible tosmoothly insert an insertion section (flexible tube) of the endoscopeinto an internal curved portion of a patient in a safe manner.Therefore, the flexible tube as described above makes it possible for anoperator to insert the insertion section with easy manipulation, thusenabling the reduction of the burden on the patient during theendoscopic examination.

Furthermore, according to the present invention, a material having highelasticity is used as a constituent material for an intermediate layerof the outer cover. This makes it possible to give high flexibility to aflexible tube.

Moreover, according to the present invention, a material having highchemical resistance is used as a constituent material for an outer layerof the outer cover. This makes it possible to give high chemicalresistance to a flexible tube.

In addition, according to the present invention, a material having ahigh adhesion with a core body is used as a constituent material for aninner layer of the outer cover. This makes it possible to give highdurability to a flexible tube.

Finally, it is to be understood that many changes and additions may bemade to the embodiments described above without departing from the scopeand spirit of the invention as defined in the appended Claims.

Further, it is also to be understood that the present disclosure relatesto subject matter contained in Japanese Patent Application Nos.2000-134922, 2000-142206 and 2000-156783 (filed on May 8, 15 and 26,2000, respectively) which are expressly incorporated herein by referencein its entirety.

TABLE 1 Inner Layer Intermediate Layer Outer Layer Thickness ThicknessThickness Chemical Material* [mm] Material* [mm] Material* [mm]Resistance Flexibility Durability Ex. 1a M 0.3 L 0.2 H1 0.1 A A A Ex. 1bM 0.2 L 0.2 H1 0.1 A A A Ex. 1c M 0.3 L 0.1 H1 0.1 A A A Ex. 1d M 0.3 L0.2 H2 0.05 A A A Ex. 1e M 0.3 L 0.2 H3 0.1 A A A Co. Ex. 1a M 0.3 — — L0.2 D C B Co. Ex. 1b M 0.3 — — H1 0.2 A D B Co. Ex. 1c H1 0.2 — — M 0.3C D D Co. Ex. 1d L 0.3 — — H1 0.2 A C D Material M: Medium HardnessPolyurethane-Based Elastomer (Hardness*: 81) Material L: Low HardnessPolyurethane-Based Elastomer (Hardness*: 68) Material H1: High HardnessPolyester-Based Elastomer (Hardness*: 92) Material H2: High HardnessPolyolefine-Based Elastomer (Hardness*: 91) Material H3: High HardnessPolyurethane-Based Elastomer (Hardness*: 92) *Hardness of the materialwas measured in accordance with JIS K 7311.

TABLE 2 Intermediate Outer Inner Layer Layer Layer Example Material MMaterial L Material H1 2a Example Material M Material L Material H1 2bExample Material M Material L Material H1 2c Example Material M MaterialL Material H2 2d Example Material M Material L Material H3 2e Co.Example Material M — Material L 2a Co. Example Material M — Material H12b Co. Example Material H1 — Material H2 2c Material M: Medium HardnessPolyurethane-Based Elastomer (Hardness*: 81) Material L: Low HardnessPolyurethane-Based Elastomer (Hardness*: 68) Material H1: High HardnessPolyester-Based Elastomer (Hardness*: 92) Material H2: High HardnessPolyolefine-Based Elastomer (Hardness*: 91) Material H3: High HardnessPolyurethane-Based Elastomer (Hardness*: 92) *Hardness of the materialwas measured in accordance with JIS K 7311.

TABLE 3 First Second Third Fourth Fifth Sixth Seventh Eighth SectionSection Section Section Section Section Section Section Example 1 1.11.3 1.4 1.5 1.6 1.8 1.9 2a Example 1 1.2 1.4 1.6 1.8 1.9 2.1 2.3 2bExample 1 1 1.5 1.5 1.8 1.8 2.2 2.2 2c Example 1 1.3 1.5 1.7 1.9 2.1 2.32.4 2d Example 1 1.1 1.3 1.4 1.5 1.6 1.8 1.9 2e

TABLE 4 Chemical Operationability Resistance Durability Example A A A 2aExample A A A 2b Example A A A 2c Example A A A 2d Example A A A 2e Co.Example C D B 2a Co. Example D A B 2b Co. Example D A D 2c

TABLE 5 First Second Third Fourth Fifth Sixth Seventh Eighth NinthSection Section Section Section Section Section Section Section SectionExample 1 1.02 1.2 1.2 1.2 1.4 1.4 1.4 1.4 3a Example 1 1.04 1.11 1.21.2 1.3 1.38 1.39 1.4 3b Example 1 1.03 1.08 1.17 1.18 1.26 1.35 1.361.38 3c Example 1 1.06 1.12 1.19 1.27 1.34 1.38 1.4 1.42 3d

TABLE 6 Chemical Operationability Resistance Durability Example A A A 3aExample A A A 3b Example A A A 3c Example A A A 3d Co. Example C D B 3aCo. Example D A B 3b Co. Example D A D 3c

1. A flexible tube for an endoscope, comprising: an elongated tubularcore body; and an outer cover which is provided over the core body, theouter cover having a portion which is formed into a laminate structurecomposed of at least three layers, wherein at least one of the layersconstituting the portion of the laminate structure has athickness-varying region where the thickness of the layer varies in itslongitudinal direction, wherein the thickness-varying region extendssubstantially over an entire region of the layer, and within thethickness-varying region the thickness of the layer varies in itslongitudinal direction in a stepwise manner including multiple steps. 2.The flexible tube as claimed in claim 1, wherein the layer with thethickness-varying region has at least one uniform thickness region whichis formed so as to adjoin the thickness-varying region.
 3. The flexibletube as claimed in claim 1, wherein the layer having thethickness-varying region is formed of a material that is different frommaterials constituting the other layers in its hardness.
 4. The flexibletube as claimed in claim 1, wherein each of at least two of the layersconstituting the portion of the laminate structure has athickness-varying region where the thickness of the layer varies in itslongitudinal direction.
 5. The flexible tube as claimed in claim 1,wherein the outer cover is provided over the core body through anextrusion molding process.
 6. The flexible tube as claimed in claim 5,wherein in the extrusion molding process a constituent material for eachof the layers is fed at a predetermined feeding rate while the core bodyis fed at a predetermined feeding speed, in which the thickness of thelayer having the thickness-varying region is controlled by adjusting thefeeding rate of the material for the layer during the extrusion moldingprocess and/or adjusting the feeding speed of the core body during theextrusion molding process.
 7. The flexible tube as claimed in claim 1,wherein the thickness-varying region varies in thickness in four stepsalong its longitudinal direction.
 8. The flexible tube as claimed inclaim 1, wherein the layer having the thickness-varying regioncomprises: a thinnest region extending through a first quarter of thelayer, which is provided toward an end tip thereof; and a thickestregion extending through a fourth quarter of the layer, which isprovided toward a base end thereof.
 9. The flexible tube as claimed inclaim 8, wherein a thickness ratio of the thinnest region over thethickest region is 0.125.
 10. The flexible tube as claimed in claim 8,wherein the thinnest region is 0.05 mm in thickness, and the thickestregion is 0.4 mm in thickness.
 11. The flexible tube as claimed in claim1, wherein an intermediate layer varies in thickness in four steps alongits longitudinal direction.
 12. The flexible tube as claimed in claim 1,wherein an intermediate layer comprises: a thickest region extendingthrough a first quarter of the layer, which is provided toward an endtip thereof; and a thinnest region extending through a fourth quarter ofthe layer, which is provided toward a base end thereof.
 13. The flexibletube as claimed in claim 12, wherein a thickness ratio of the thinnestregion over the thickest region is 0.125.
 14. The flexible tube asclaimed in claim 12, wherein the thinnest region is 0.05 mm inthickness, and the thickest region is 0.4 mm in thickness.
 15. Aflexible tube for an endoscope, comprising: an elongated tubular corebody; and an outer cover which is provided over the core body, the outercover having a portion which is formed into a laminate structurecomposed of at least three layers, wherein at least one of the layersconstituting the portion of the laminate structure has at least threeregions and at least two boundary parts along its longitudinaldirection, and one of the regions is contiguous to the other regionthrough one of the boundary parts, in which one of the regions isdifferent from the other regions adjacent thereto in its physicalproperty and/or chemical property, wherein each of the boundary parts isformed as a property-varying part within which the physical propertyand/or the chemical property of the layer gradually vary in itslongitudinal direction.
 16. The flexible tube as claimed in claim 15,wherein one of the regions is formed of a material which is differentfrom that forming the other region adjacent thereto.
 17. The flexibletube as claimed in claim 15, wherein each of at least two of the layersconstituting the portion of the laminate structure has at least tworegions and at least one boundary part along its longitudinal direction,and one of the regions is contiguous to the other region through theboundary part, in which one of the regions is different from the otherregion adjacent thereto in its physical property and/or chemicalproperty.
 18. The flexible tube as claimed in claim 17, wherein theouter cover is formed such that the boundary part of one layer is notlocated above or below the boundary part of the other layer in itsthickness direction.
 19. The flexible tube as claimed in claim 15,wherein the boundary part is formed of a mixture of a materialconstituting one of the regions and a material constituting the otherregion.
 20. The flexible tube as claimed in claim 15, wherein in thelayer having the at least three regions, one of the regions is differentfrom the other region adjacent thereto in its hardness.
 21. The flexibletube as claimed in claim 15, wherein the flexible tube has tip and baseends, and flexibility of the flexible tube increases in a gradual orstepwise manner along the direction from the base end to the tip end.22. The flexible tube as claimed in claim 15, wherein the layers of thelaminate structure include an inner layer, an outer layer and at leastone intermediate layer formed between the inner layer and the outerlayer, and wherein the intermediate layer of the outer cover has ahigher elasticity than the inner and outer layers so that theintermediate layer functions as cushioning between the inner layer andthe outer layer.
 23. The flexible tube as claimed in claim 15, whereinat least one of the layers constituting the portion of the laminatestructure has a thickness-varying region where the thickness of thelayer varies in its longitudinal direction.
 24. A flexible tube for anendoscope, comprising: an elongated tubular core body; and an outercover which is provided over the core body, the outer cover having aportion which is formed into a laminate structure composed of at leastthree layers, wherein at least one of the layers constituting theportion of the laminate structure has at least three regions and atleast two boundary parts along its longitudinal direction, and one ofthe regions is contiguous to the other region through one of theboundary parts, in which one of the regions is different from the otherregions adjacent thereto in its physical property and/or chemicalproperty, wherein the layer having the boundary parts is formed suchthat the physical property and/or the chemical property within each ofthe boundary parts vary in its longitudinal direction in a substantiallystepwise manner.
 25. The flexible tube as claimed in claim 24, whereinthe layers of the laminate structure include an inner layer, an outerlayer and at least one intermediate layer formed between the inner layerand the outer layer, and wherein the intermediate layer of the outercover has a higher elasticity than the inner and outer layers so thatthe intermediate layer functions as cushioning between the inner layerand the outer layer.